Iowa - Criteria: C (architecture/engineering)
| Lake City Water Standpipe |
| Lake, John, House |
| Lakeside Park Historic District |
| Lamberson, Jack, House |
| Lamb, Lafayette, House |
| Lamm-Pollmiller Farmstead District |
| Lancaster School |
| Land and Loan Office Building |
| Lane, Samuel M., House |
| Lange, August H. J. and Justena, Farmstead Historic District |
| Langworthy Historic District |
| Langworthy House |
| Lansing Main Street Historic District |
| Lansing Stone School |
| Larsen, Chris, House |
| Larsen, Jens T., House |
| Lattner Auditorium Building |
| Laurens Carnegie Free Library |
| Lawrence Bridge |
| LeClaire, Antoine, House |
| Lee, Captain Daniel S. and Fannie L. (Brooks), House |
| Leeds Junior High School |
| Leet, William A., and Frederick Hassler Farmstead District |
| Le Grand Bridge |
| Le Grand Bridge |
| Le Mars Central High School |
| Le Mars Municipal Park and Golf Course Historic District |
| Le Mars Public Library |
| Lenox Round Barn |
| Lerch, Gustov C., House |
| Lesinger Block |
| Lewis Hotel |
| Lexington, The |
| Liberty Building |
| Liberty Hall |
| Lincoln Elementary School |
| Lincoln-Fairview Historic District |
| Lincoln School |
| Lincoln School |
| Lincoln Township Mausoleum |
| Linden Flats |
| Linden Heights Historic District |
| Lindsay, James E., House |
| Linsay House |
| Lippert House |
| Lippincott, John, House |
| Lisbon Methodist Church |
| Littig, John, House |
| Little Sioux River Bridge |
| Lock and Dam No. 11 Historic District |
| Lock and Dam No. 16 Historic District |
| Lock and Dam No. 19 Historic District |
| """Lockkeeper's"" House" |
| Locust School |
| Loetscher, T. Ben, House |
| Logan Center School No.5 |
| LONESTAR |
| Longfellow Historic District |
| Long, J. G. and Regina, House |
| Loucks Grove Church |
| Louisa Building |
| Louisa County Courthouse |
| Lower Road Bridge |
| Lubben, Henry, House, Smokehouse and Springhouse |
| Lucas County Courthouse |
| Lucas County Courthouse Square Historic District |
| Luedtke, August and Vera, Barn |
| Lueschen, John, House |
| Lustron Home #02102 |
| Luther College Farm |
| Lu Verne City Jail |
| Lyon Block |
| Lyon County Courthouse |
| Maas Commercial Building |
| MacDonald, Gilmour B. and Edith Craig, House |
| Mack-International Motor Truck Corporation Building |
| Macumber, John Andrew and Sara, Ice House |
| Madison County Courthouse |
| Mahaska County Courthouse |
| Mahnke House |
| Maine, The |
| Main Street Bridge |
| Maish House |
| Malek Theatre |
| Mallet, Joseph, House |
| Mallory Township Bridge |
| Manning Commercial Historic District |
| Manning Water Tower |
| Mann School No. 2 |
| Manufacturing and Wholesale Historic District |
| Maquoketa Caves State Park Historic District |
| Maquoketa Company-Clinton Machine Company Administration Building |
| Maquoketa Free Public Library |
| Marion Carnegie Public Library |
| Marion Commercial Historic District |
| Marion County Courthouse |
| Marshall County Courthouse |
| Marshalltown Downtown Historic District |
| Marsh, E.A. and Rebecca (Johnson), House |
| Mars Hill |
Data from United States Park Service and Wikidata
