Iowa - Area of significance: Architecture
| 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 |
| """Lockkeeper's"" House" |
| Locust School |
| Loetscher, T. Ben, House |
| Logan Center School No.5 |
| Longfellow Historic District |
| Long, J. G. and Regina, House |
| Loras College Historic District |
| Loucks Grove Church |
| Louisa Building |
| Louisa County Courthouse |
| Louis F. and Emma M. (Edler) Wohlert House-Emma Wohlert Maternity Home |
| 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 |
| Lustron House #02437 |
| Luther A. and Elinore T. Brewer House |
| Luther College Campus Historic District |
| 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 |
| Maish House |
| Malek Theatre |
| Mallet, Joseph, House |
| Manning Commercial Historic District |
| 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 |
| Marsh-Place Building |
| Martin, Abner, House |
| Martin, Dr. G. S., House |
| Martin Hotel |
| Martin, S. F., House |
| Martzahn, August F., House |
| Marycrest College Historic District |
| Mary Elizabeth Day Nursery |
| Mason City Downtown Historic District |
| Mason City Engine House No. 2 |
| Mason City Public Library |
| Masonic Temple Building |
| Masonic Temple of Des Moines |
| Masonic Temple Theater |
| Masters Building |
| Master Service Station |
| Matt-Bahls House |
| Mattes, Minnie Y. and Frank P., House |
| May's Island Historic District |
| MBA (Modern Brotherhood of America) Building |
| McBride, Charles H. & Theresa H., Bungalow |
| McBride-Hickey House |
| McCaffrey House |
| McCandless Building |
| McCarthy, Patrick F., House |
| McCartney, James H. and Mayetta (Degrush), House |
| McClaine House |
| McClanahan Block |
| McCleery Calendar Factory |
| McClellan Heights Historic Dictrict |
| McClellan's General Store |
| McClung, J. J., House |
| McCollister, James, Farmstead |
| McColm, Laura Musser, Historic District |
| McConn, Daniel, Barn |
| McDonald House |
| McElhinny House |
| McGee School |
| McGreer, John, Barn and Crib |
| McGregor Commercial Historic District |
| McHarg, Joseph S., House |
| McHenry, William A., House |
| McKibben, S. M., House |
Data from United States Park Service and Wikidata
