Iowa - Significance region: Local
| McGee School |
| McGreer, John, Barn and Crib |
| McGregor Commercial Historic District |
| McHaffey Opera House |
| McHarg, Joseph S., House |
| McHenry, William A., House |
| McKibben, S. M., House |
| McKinley Elementary School |
| McKinney House |
| McMahon House |
| McManus House |
| McMullin, Maj. James W., House |
| McNeill, W.A., House |
| McQuie, Peter and Isabelle McCulloch, Milkhouse |
| McQuilken, John N. and Mary, House |
| McWaid, Job A. and Rebecca E., House |
| Meadly House |
| Mears Hall |
| Meek's Flour Mill |
| Meiser Drug Store |
| Melcher, Dennis Melcher, Pottery and House |
| Mellinger Memorial Library |
| Memorial Building |
| Mentzer, Joseph P., House |
| Merrero Building |
| Methodist Deaconess Institute-Esther Hall |
| Metropolitan Opera House |
| Metz Manufacturing Company |
| Meyers Farmstead Historic District |
| Middlefork Methodist Episcopal Church |
| Middlesex Plat Historic District |
| Middleton, Dr. George McLelland, House and Garage |
| Miller Building |
| Miller, F. H., House |
| Miller, Severin, House |
| Mill Rock School |
| Milwaukee and St. Paul Railway Combination Depot |
| Minburn Railroad Depot |
| Minor, Josias L. and Elizabeth A., Farmstead District |
| Missouri, Iowa & Nebraska Railway Co. Depot-Weldon |
| Mitchell-Maskrey Mill |
| Mitchell Powerhouse and Dam |
| Modale School and Masonic Hall |
| Moeszinger-Marquis Hardware Co. |
| Monona County Courthouse |
| Monroe County Courthouse |
| Monroe Elementary School Historic District |
| Montezuma Downtown Historic District |
| Montgomery County Courthouse |
| Montgomery County Jail |
| Moorehead Stagecoach Inn |
| Moore, Josiah B. and Sara, House |
| Moorhead, Joseph and Clara Amanda H., House |
| Morningside College Historic District |
| Motie, Joseph, House |
| Motor Mart Building |
| Motor Mill Historic District |
| Motor Townsite |
| Mount Sinai Temple |
| Mount Vernon Commercial Historic District |
| Moyce-Steffens House |
| Mulcahy Barn |
| Municipal Auditorium |
| Municipal Building |
| Municipal Building |
| Murillo Flats |
| Murray General Merchandise Store |
| Murray, Thomas, House |
| Muscatine Avenue Moffitt Cottage Historic District |
| Muscatine County Courthouse |
| Muscatine County Home Dairy Barn |
| Mylius-Eaton House |
| National Biscuit Company Building |
| National State Bank |
| Naylor House |
| Neessen, Chris, House |
| Nelson, Daniel, House and Barn |
| Netcott-Pfeiffer House |
| Nevada Downtown Historic District |
| New Carroll House Hotel |
| Newcome, Daniel T., Double House |
| Newens Sanitary Dairy Historic District |
| New Era Building |
| Newhall, Lucian, House |
| New Lawn, The |
| New Orpheum Theatre |
| New Providence Building Association Stores |
| New Providence School Gymnasium |
| New Sweden Chapel |
| Newton Downtown Historic District |
| Newton, James P., House and Maid Cottage |
| Nichols, Benjamin F. and Susan M. (Jenkins), House |
| Nichols, Oscar, House |
| Nichols, Samuel, House |
| Nichols, William Anzi, House |
| Nicking House |
| Nicolaus, Henry E. and Ella M. (Knott), House |
| Niemann, Theodore, House and Spring House |
| Nighswander, Benjamin, House |
| Nishnabotna Ferry House |
Data from United States Park Service and Wikidata
