UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number: 
     811-21178               

               BlackRock Insured Municipal Income Trust               
(Exact name of registrant as specified in charter)

100 Bellevue Parkway, Wilmington, DE
 
19809
(Address of principal executive offices)
 
(Zip code)

Robert S. Kapito, President

 
BlackRock Insured Municipal Income Trust
40 East 52nd Street, New York, NY 10022
(Name and address of agent for service)

Registrant's telephone number, including area code: 
     888-825-2257

Date of fiscal year end:
     August 31, 2007     
Date of reporting period: 
     May 31, 2007     

Item 1. Schedule of Investments.

The Registrant’s unaudited schedule of investments as of the close of the reporting period pursuant to Rule 30b1-5 under the Investment Company Act of 1940 is as follows:

PORTFOLIO OF INVESTMENTS (unaudited)
MAY 31, 2007
BlackRock Insured Municipal Income Trust (BYM)
(Percentages shown are based on Net Assets)

Principal                
Amount      
Option Call
       
(000)       Description      
Provisions1
       
Value
    LONG-TERM INVESTMENTS—154.8%            
    Alabama—0.7%            
$      2,800   Jefferson Cnty. Ltd. Oblig., Sch. Impvts. Sales Tax RB, Ser. A, 4.75%,            
       1/01/25   01/14 @ 100  
$
2,836,204 
    Arizona—2.6%            
10,000   Phoenix Civic Impvt. Corp., Pub. Impvts. Sales Tax RB, Civic Plaza            
       Expansion Proj., 5.00%, 7/01/41, FGIC   07/15 @ 100  
 
10,362,700 
    California—32.4%            
2,000   Arcadia Unified Sch. Dist., Sch. Impvts. Ad Valorem Ppty. Tax GO, Zero            
       Coupon, 8/01/28, FSA   02/17 @ 33.207       410,240  
3,380   Chabot Las Positas Cmnty. Coll. Dist., Univ. & Coll. Impvts. Ad Valorem            
       GO, Zero Coupon, 8/01/25, AMBAC   08/16 @ 64.511     1,411,623  
14,000 2 Dept. of Wtr. Recs. Cash Flow Mgmt., Elec., Pwr. & Lt. RB, Ser. A,            
       5.375%, 5/01/12   N/A     15,102,780  
    Golden St. Tobacco Sec. Corp.,            
6,500 2    Misc. Purps. Tobacco Settlement Funded RB, Ser. A-1, 6.625%, 6/01/13   N/A     7,435,740  
14,500 2    Misc. Purps. Tobacco Settlement Funded RB, Ser. A-1, 6.75%, 6/01/13   N/A     16,683,555  
10,100 2 Infrastructure & Econ. Dev. Bank, Hwy. Impvts. Tolls RB, Bay Area Toll            
       Brdgs. Proj., Ser. A, 5.00%, 1/01/28, AMBAC   N/A     11,190,901  
17,500   Met. Wtr. Dist. of Southern California, Wtr. Util. Impvts. RB, Ser. B-1,            
       5.00%, 10/01/33, FGIC   10/13 @ 100     18,221,175  
2,700   Sacramento City Unified Sch. Dist., Sch. Impvts. Ad Valorem GO, 5.00%,            
       7/01/30, MBIA   07/15 @ 100     2,831,571  
15,000   San Francisco City & Cnty. Pub. Utils. Comm., Wtr. Util. Impvts. RB, Ser.            
       A, 5.00%, 11/01/31, FSA   11/11 @ 100     15,417,750  
53,000   San Joaquin Hills Transp. Corridor Agcy., Hwy. Tolls RB, Ser. A, Zero            
       Coupon, 1/15/31, MBIA   No Opt. Call     17,893,330  
400   San. Mateo Union High Sch. Dist., Sch. Impvts. Lease Abatement COP,            
       Zero Coupon, 12/15/43, AMBAC   12/24 @ 100     221,144  
    Univ. of California, Univ. & Coll. Impvts. RB,            
10,000      Ser. C, 4.75%, 5/15/37, MBIA   05/13 @ 101     10,177,600  
3,330      Ser. G, 4.75%, 5/15/31, MBIA   05/13 @ 101     3,397,133  
10,000 2    Ser. O, 5.00%, 9/01/10, FGIC   N/A  
 
10,473,400  
           
 
130,867,942  
    District of Columbia—3.1%            
2,000   Dist. of Columbia, Ad Valorem Ppty. Tax GO, Ser. A, 4.75%, 6/01/36,            
       FGIC   06/17 @ 100     2,023,840  
9,500   Tobacco Settlement Fing. Corp., Tobacco Settlement Funded RB, 6.75%,            
       5/15/40   05/11 @ 101  
 
10,420,170  
           
 
12,444,010  
    Florida—7.0%            
3,600   City of Tampa, Wtr. Util. Impvts. Wtr. RB, 4.625%, 10/01/36, MBIA   10/16 @ 100     3,562,704  
    Cnty. of Miami-Dade,            
9,500      Aviation, Port, Arpt. & Marina RB, Miami Intl. Arpt. Proj., Ser. B,            
       5.00%, 10/01/37, FGIC   10/14 @ 100     9,811,315  
25,520      Recreational Fac. Impvts. Misc. RB, Cap. Apprec. Proj., Ser. A, Zero            
       Coupon, 10/01/38, MBIA   10/15 @ 30.363     5,193,320  
5,485   Cnty. of Orange, Sales Tax RB, 4.75%, 10/01/32, XLCA   10/16 @ 100     5,552,794  
2,300   Highlands Cnty. Hlth. Facs. Auth., Hlth., Hosp. & Nursing Home Impvts.            
       RB, Adventist Bolingbrook Hlth. Sys. Proj., 5.125%, 11/15/32   11/16 @ 100     2,356,235  
1,880   JEA, Wtr. Util. Impvts. Wtr. RB, Ser. A, 4.75%, 10/01/36, MBIA   04/11 @ 100  
 
1,902,203  
           
 
28,378,571  
    Georgia—3.9%            
    City of Atlanta,            
800      Port, Arpt. & Marina Impvts. RB, Ser. J, 5.00%, 1/01/34, FSA   01/15 @ 100     829,072  
2,000      Wtr. & Wstwtr., Wtr. Util. Impvts. RB, 5.00%, 11/01/34, FSA   11/14 @ 100     2,081,580  
9,555      Wtr. RB, Ser. A, 5.00%, 11/01/38, FGIC   05/09 @ 101     9,625,516  
3,235      Wtr. Util. Impvts. RB, 5.00%, 11/01/37, FSA   11/14 @ 100  
 
3,362,815  
           
 
15,898,983  
    Illinois—15.8%            
11,550   City of Chicago, Hwy. Impvts. RB, 5.25%, 1/01/27, AMBAC   01/11 @ 101     12,084,765  
    Met. Pier & Exposition Auth.,            
24,010      Pub. Impvts. Sales Tax RB, McCormick Place Expansion Proj., Ser. A,            
       5.00%, 12/15/28, MBIA   06/12 @ 101     24,856,352  

1

BlackRock Insured Municipal Income Trust (BYM) (continued)
(Percentages shown are based on Net Assets)

Principal                
Amount              
Option Call
           
(000)   Description  
Provisions1
   
Value 
    Illinois— (cont'd)            
$      15,000      Sales Tax RB, McCormick Place Expansion Proj., Ser. B, Zero Coupon,            
       6/15/28, MBIA   No Opt. Call   $ 5,785,350  
6,165   Mun. Elec. Agcy., Elec., Pwr. & Lt. RB, 4.50%, 2/01/35, FGIC   02/16 @ 100       6,012,170  
14,875   Vlg. of Bolingbrook, Ad Valorem Ppty. Tax GO, Ser. A, 4.75%, 1/01/38,            
       MBIA   01/15 @ 100  
 
15,072,986  
           
 
63,811,623  
    Indiana—1.2%            
4,725   Mun. Pwr. Agcy., Elec., Pwr. & Lt. Impvts. RB, Pwr. Sply. Sys. Proj., Ser.            
       A, 4.50%, 1/01/32, AMBAC   01/16 @ 100  
 
4,635,225  
    Kansas—0.4%            
1,750   Univ. of Kansas Hosp. Auth., Hlth., Hosp. & Nursing Home RB, Univ. of            
       Kansas Hlth. Sys. Proj., 5.00%, 9/01/36   09/16 @ 100  
 
1,774,465  
    Louisiana—4.4%            
12,100   Hwy. Impvts. Fuel Sales Tax RB, Ser. A, 4.75%, 5/01/39, FSA   05/16 @ 100     12,248,709  
5,450   Hwy. Impvts. Sales Tax RB, Ser. A, 5.00%, 5/01/35, FGIC   05/15 @ 100  
 
5,673,777  
           
 
17,922,486  
    Massachusetts—8.3%            
10,190   Bay Transp. Auth., Sales Tax RB, Ser. A-2, Zero Coupon, 7/01/32   07/17 @ 49.09     2,996,166  
24,000   Tpke. Auth. Met. Hwy. Sys., Hwy. Tolls RB, Ser. A, 5.00%, 1/01/39,            
       AMBAC   01/09 @ 101     24,417,600  
5,985   Wtr. Recs. Auth., Wtr. RB, Ser. A, 5.00%, 8/01/41   08/16 @ 100  
 
6,216,500  
           
 
33,630,266  
    Michigan—0.6%            
1,415   Detroit, Swr. Impvts. RB, 5.00%, 7/01/32, FSA   07/13 @ 100     1,464,369  
1,000   St. Hosp. Fin. Auth., Hlth., Hosp. & Nursing Home RB, Oakwood Hlth.            
       Care Sys. Proj., 5.00%, 7/15/25   07/17 @ 100  
 
1,018,240  
           
 
2,482,609  
    Missouri—1.0%            
4,100   Joint Mun. Elec. Util. Comm., Elec., Pwr. & Lt. Impvts. RB, Plum Point            
       Proj., 4.60%, 1/01/36, MBIA   01/16 @ 100  
 
4,062,485  
    Nebraska—1.1%            
4,280   Omaha Pub. Pwr. Dist., Elec., Pwr. & Lt. Impvts. RB, Ser. A, 4.75%,            
       2/01/44   02/14 @ 100  
 
4,304,054  
    Nevada—9.0%            
6,000 2 Reno, Misc. Taxes RB, Reno Transp. Proj., 5.125%, 6/01/12, AMBAC   N/A     6,322,620  
    Truckee Meadows Wtr. Auth.,            
7,500      Wtr. RB, 4.875%, 7/01/34, XLCA   07/16 @ 100     7,679,400  
10,000 2    Wtr. Util. Impvts. RB, Ser. A, 5.00%, 7/01/11, FSA   N/A     10,426,500  
6,500 2    Wtr. Util. Impvts. RB, Ser. A, 5.125%, 7/01/11, FSA   N/A     6,807,645  
5,000 2    Wtr. Util. Impvts. RB, Ser. A, 5.25%, 7/01/11, FSA   N/A  
 
5,260,050  
           
 
36,496,215  
    New York—4.4%            
7,305   New York City Mun. Wtr. Fin. Auth., Wtr. RB, Ser. C, 5.00%, 6/15/35,            
       AMBAC   06/14 @ 100     7,599,099  
10,000   New York City Trust for Cultural Recs., Recreational RB, American            
       Museum of Natural History Proj., Ser. A, 5.00%, 7/01/44, MBIA   07/14 @ 100  
 
10,338,600  
           
 
17,937,699  
    Ohio—2.5%            
10,000   Air Qual. Dev. Auth., Rec. Recovery RB, Dayton Pwr. & Lt. Co. Proj.,            
       4.80%, 1/01/34, FGIC   07/15 @ 100  
10,134,700  
   
    Pennsylvania—2.0%            
2,500   Lebanon Cnty. Hlth. Facs. Auth., Hlth., Hosp. & Nursing Home RB, Good            
       Samaritan Hosp. Proj., 6.00%, 11/15/35   11/12 @ 101     2,701,700  

2

BlackRock Insured Municipal Income Trust (BYM) (continued)
(Percentages shown are based on Net Assets)

Principal                
Amount          
Option Call
       
(000)  
Description
     
Provisions1
       
Value  
    Pennsylvania— (cont'd)            
$      5,200 2 Philadelphia Gas Wks., Natural Gas Util. Impvts. RB, Ser. 3, 5.125%,            
       8/01/11, FSA   N/A  
$
5,443,932  
           
   
8,145,632  
    South Carolina—8.5%            
5,000 2 Pub. Svc. Auth., Elec., Pwr. & Lt. RB, Ser. B, 5.50%, 1/01/12, FSA   N/A     5,334,800  
4,000   Scago Edl. Facs Corp. for Colleton Sch. Dist., Sch. Impvts. Lease Approp.            
       RB, Pickens Cnty. Proj., 5.00%, 12/01/31, FSA   12/16 @ 100     4,172,080  
    Transp. Infrastructure Bank,            
12,750      Fuel Sales Tax RB, Ser. A, 5.00%, 10/01/33, AMBAC   10/12 @ 100     13,207,470  
11,000 2    Trans. Impvts. RB, Ser. B, 5.125%, 10/01/11, AMBAC   N/A  
 
11,545,270  
           
 
34,259,620  
    Tennessee—4.7%            
    Knox Cnty. Hlth., Edl. & Hsg. Facs. Brd., Hlth., Hosp. & Nursing Home            
    RB, Covenant Hlth. Proj.,            
10,000      Zero Coupon, 1/01/41   01/17 @ 30.07     1,737,400  
11,705      Ser. A, Zero Coupon, 1/01/22, FSA   01/13 @ 59.566     5,393,898  
9,260      Ser. A, Zero Coupon, 1/01/23, FSA   01/13 @ 56.016     4,008,562  
8,500      Ser. A, Zero Coupon, 1/01/24, FSA   01/13 @ 52.749     3,461,540  
6,850      Ser. A, Zero Coupon, 1/01/25, FSA   01/13 @ 49.712     2,626,290  
5,000      Ser. A, Zero Coupon, 1/01/26, FSA   01/13 @ 46.781  
 
1,799,150  
           
 
19,026,840  
    Texas—27.3%            
    City of San Antonio, Wtr. RB,            
9,350      5.125%, 5/15/29, FGIC   05/14 @ 100     9,788,141  
10,000      5.125%, 5/15/34, FGIC   05/14 @ 100     10,432,000  
    Cnty. of Harris, Ad Valorem Ppty. Tax GO,            
7,485      Zero Coupon, 8/15/25, MBIA   No Opt. Call     3,287,936  
10,915      Zero Coupon, 8/15/28, MBIA   No Opt. Call     4,143,661  
10,030   Coppell Indpt. Sch. Dist., Ad Valorem Ppty. Tax GO, Zero Coupon,            
       8/15/30, PSF   No Opt. Call     3,451,724  
2,350 2 Dallas Area Rapid Trans., Sales Tax RB, 5.00%, 12/01/11, AMBAC   N/A     2,457,724  
5,510   Harris Cnty., Hwy. Tolls RB, 5.00%, 8/15/30, FSA   08/12 @ 100     5,700,811  
    Harris Cnty.-Houston Sports Auth.,            
5,785      Hotel Occupancy Tax RB, Ser. H, Zero Coupon, 11/15/38, MBIA   11/31 @ 64.91     1,152,141  
6,160      Hotel Occupancy Tax RB, Ser. H, Zero Coupon, 11/15/39, MBIA   11/31 @ 60.976     1,150,010  
26,890      Lease RB, Ser. A-3, Zero Coupon, 11/15/38, MBIA   11/24 @ 43.826     5,121,201  
27,675      Lease RB, Ser. A-3, Zero Coupon, 11/15/39, MBIA   11/24 @ 41.258     4,955,209  
2,000   Hlth. Care Facs. Auth., Hlth., Hosp. & Nursing Home RB, Providence            
       Hlth. Care Svcs. Proj., 4.50%, 10/01/35, FGIC   10/16 @ 100     1,931,520  
5,315   Lewisville Indpt. Sch. Dist., Sch. Impvts. Ad Valorem Ppty. Tax GO, Zero            
       Coupon, 8/15/24, FGIC   08/15 @ 66.003     2,334,667  
6,000   Lower Colorado River Auth., Misc. RB, 4.75%, 5/15/36, AMBAC   05/11 @ 100     6,036,420  
1,045   Montgomery Cnty. Mun. Util. Dist. No. 46, Pub. Impvts. Ad Valorem            
       Ppty. Tax GO, 4.75%, 3/01/30, MBIA   03/14 @ 100     1,055,147  
9,500   Northside Indpt. Sch. Dist., Sch. Impvts. Ad Valorem Ppty. Tax GO,            
       5.125%, 6/15/29, PSF   06/14 @ 100     9,949,730  
3,000   Pearland, Ad Valorem Ppty. Tax GO, 4.75%, 3/01/29, FGIC   03/16 @ 100     3,053,550  
30,145   Tpke. Auth., Hwy. Impvts. Tolls RB, Ser. A, 5.00%, 8/15/42, AMBAC   08/12 @ 100     30,877,825  
3,000 2 Tyler Cnty. Hlth. Facs. Dev., Hlth., Hosp. & Nursing Home Impvts. RB,            
       Mother Frances Hosp. Proj., 6.00%, 7/01/12   N/A  
 
3,264,780  
           
 
110,144,197  
    Virginia—3.4%            
    Chesterfield Cnty. Indl. Dev. Auth.,            
3,000      Indl. Impvts. RB, Elec. & Pwr. Co. Proj., Ser. A, 5.875%, 6/01/17   11/10 @ 102     3,198,210  
4,000      Indl. RB, Elec. & Pwr. Co. Proj., Ser. B, 5.875%, 6/01/17   11/10 @ 102     4,282,880  
6,000   Stafford Cnty. Econ. Dev. Auth., Hlth., Hosp. & Nursing Home Impvts.            
       RB, Medicorp Hlth. Sys. Oblig. Proj., 5.25%, 6/15/37   06/16 @ 100  
 
6,213,780  
           
 
13,694,870  
    Washington—10.2%            
9,610   Central Washington Univ., Coll. & Univ. RB, 5.00%, 5/01/34, FGIC   05/14 @ 100     9,950,290  
3,655   Chelan Cnty. Pub. Util. Dist. 1, Elec., Pwr. & Lt. RB, Chelan Hydro Sys.            
       Proj., Ser. C, 5.125%, 7/01/33, AMBAC   07/12 @ 100     3,773,203  

3

BlackRock Insured Municipal Income Trust (BYM) (continued)
(Percentages shown are based on Net Assets)

Principal                
Amount       Option Call        
(000)      
Description
  Provisions1        
Value  
    Washington— (cont'd)            
$     2,200
  Cnty. of King, Swr. RB, 5.00%, 1/01/36, FSA   01/16 @ 100   $ 2,290,244  
4,110
  Hlth. Care Facs. Auth., Hlth., Hosp. & Nursing Home RB, Providence              
     Hlth. Sys. Proj., Ser. A, 4.625%, 10/01/34, FGIC   10/16 @ 100     4,043,952  
4,500
  Port of Seattle, Port, Arpt. & Marina RB, Ser. A, 5.00%, 4/01/31, FGIC   10/11 @ 100     4,637,430  
6,380
  Pub. Impvts. Misc. GO, Ser. A, 5.00%, 7/01/25, FSA   07/11 @ 100     6,588,817  
9,500
 2 Seattle, Pkg. Fac. Impvts. Ad Valorem Ppty. Tax GO, Ser. F, 5.125%,            
     12/15/08, MBIA   N/A  
 
9,701,970  
         
 
40,985,906  
  West Virginia—0.3%            
1,295
  Econ. Dev. Auth., Correctional Fac. Impvts. Lease RB, Correctional            
       Juvenile Safety Proj., Ser. A, 5.00%, 6/01/29, MBIA   06/14 @ 100  
 
1,347,707  
    Total Long-Term Investments (cost $592,367,922)      
 
625,585,009  
Shares                
(000)                
    MONEY MARKET FUND—0.5%            
1,900
 3,4     Merrill Lynch Institutional Tax Exempt Fund, 3.60% (cost $1,900,000)   N/A  
 
1,900,000  
Total Investments —155.3% (cost $594,267,9225)       $ 627,485,009  
Other assets in excess of liabilities —1.4%         5,670,401  
Preferred shares at redemption value, including dividends payable —(56.7)%      
 
(229,067,201) 
Net Assets Applicable to Common Shareholders —100%      
$
404,088,209  

 

 
1      Date (month/year) and price of the earliest optional call or redemption. There may be other call provisions at varying prices at later dates.  
 
2 This bond is prerefunded. U.S. government securities, held in escrow, are used to pay interest on this security, as well as retire the bond in full at the date indicated, typically at a premium to par.  
 
3 Represents an investment in an affiliate.  
 
4 Represents current yield as of May 31, 2007.  
 
5 Cost for federal income tax purposes is $594,245,728. The net unrealized appreciation on a tax basis is $33,239,281, consisting of $33,899,018 gross unrealized appreciation and $659,737 gross unrealized depreciation.  
 
  The value (market value plus accrued interest) of securities that are covered by insurance, which ensures the payment of principal and interest, represent approximately 85.5% of the Trust's managed assets.  
 
AMBAC
  
—
   21.8%  
FGIC
 
—
  20.5%  
FSA
 
—
  16.7%  
MBIA
 
—
  21.9%  
PSF
 
—
  2.2%  
XCLA
 
—
  2.1%  
Other
 
—
  0.3%  

 
 
KEY TO ABBREVIATIONS  
 
AMBAC
— American Municipal Bond Assurance Corp.  
MBIA
— Municipal Bond Insurance Assoc.  
COP
— Certificate of Participation  
PSF
— Public School Fund Guaranteed  
FGIC
— Financial Guaranty Insurance Co.  
RB
— Revenue Bond  
FSA
— Financial Security Assurance  
XLCA
— XL Capital Assurance  
GO
— General Obligation        
 

4

Item 2. Controls and Procedures.

(a) The Registrant's principal executive and principal financial officers have evaluated the Registrant's disclosure controls and procedures within 90 days of this filing and have concluded, as of that date, that the Registrant’s disclosure controls and procedures were reasonably designed to ensure that information required to be disclosed by the Registrant in this Form N-Q was recorded, processed, summarized, and reported within the required time periods and that information to be disclosed by the Registrant in this Form N-Q was accumulated and communicated to the Registrant’s management, including its principal executive and principal financial officers, as appropriate, to allow timely decisions regarding required disclosure.

(b) There were no changes in the Registrant's internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act (17 CFR 270.30a -3(d)) that occurred during the Registrant's last fiscal quarter that have materially affected, or are reasonably likely to materially affect, the Registrant's internal control over financial reporting.

Item 3. Exhibits.

Separate certifications of the Registrant’s Principal Executive and Financial Officers pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 are attached as EX-99.CERT.

SIGNATURES

          Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant) 
       BlackRock Insured Municipal Income Trust       
   
By: 
     /s/ Donald C. Burke
Name: Donald C. Burke
Title: Treasurer and Principal Financial Officer
Date: July 25, 2007

          Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the Registrant and in the capacities and on the dates indicated.

By: 
     /s/ Robert S. Kapito
Name: Robert S. Kapito
Title: President and Principal Executive Officer
Date: July 25, 2007
   
By: 
     /s/ Donald C. Burke
Name: Donald C. Burke
Title: Treasurer and Principal Financial Officer
Date: July 25, 2007