Iowa - Area of significance: Architecture
| 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 |
| Meadly House |
| Mears Hall |
| Meiser Drug Store |
| Melcher, Dennis Melcher, Pottery and House |
| Mellinger Memorial Library |
| Melrose Historic District |
| Mentzer, Joseph P., House |
| Merchants' National Bank |
| Merrero Building |
| Methodist Deaconess Institute-Esther Hall |
| Metropolitan Opera House |
| Meyers Farmstead Historic District |
| Middlefork Methodist Episcopal Church |
| Middlesex Plat Historic District |
| Middleton, Dr. George McLelland, House and Garage |
| Miller, Alvin, House |
| Miller Building |
| Miller, F. H., House |
| Miller, Norris, House |
| Miller, Severin, House |
| Mill Rock School |
| Mills Tower Historic District |
| Minburn Railroad Depot |
| Mini-Wakan State Park Historic District |
| Minor, Josias L. and Elizabeth A., Farmstead District |
| Mitchell County Courthouse |
| Mitchell-Maskrey Mill |
| 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 |
| Moorhead, Joseph and Clara Amanda H., House |
| Morningside College Historic District |
| Morrill Hall |
| Moser Stone House |
| Motie, Joseph, House |
| Motor Mart Building |
| Motor Mill Historic District |
| Mount Pleasant Public Library |
| Mount Saint Bernard Seminary and Barn |
| Mount Sinai Temple |
| Mount Vernon Commercial Historic District |
| Moyce-Steffens House |
| Mulcahy Barn |
| Municipal Auditorium |
| Municipal Building |
| Municipal Building |
| Munson Building |
| Murillo Flats |
| Murray General Merchandise Store |
| Murray, Thomas, House |
| Muscatine Avenue Moffitt Cottage Historic District |
| Muscatine County Courthouse |
| Mylius-Eaton House |
| 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 Providence School Gymnasium |
| Newton Downtown Historic District |
| Newton, James P., House and Maid Cottage |
| Nichols, Oscar, House |
| Nichols, Samuel, House |
| Nichols, William Anzi, House |
| Nicking House |
| Nicolaus, Henry E. and Ella M. (Knott), House |
| Nieland House |
| Niemann, Theodore, House and Spring House |
| Nighswander, Benjamin, House |
| Noble-Kendall House |
| Norris, F. M., House |
| North Fellows Historic District |
| North Grand Avenue Residential Historic District |
| North Grinnell Historic District |
| North Presbyterian Church |
| Northwest Davenport Savings Bank |
| Northwestern Hotel |
| Norton, Charles Henry and Charlotte, House |
| Oakes-Wood House |
Data from United States Park Service and Wikidata
