Iowa - Role: Building
| Marshall County Courthouse |
| 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 |
| Martin, T.S., and Company |
| Martzahn, August F., House |
| Mary Elizabeth Day Nursery |
| Mason City Engine House No. 2 |
| Mason City Public Library |
| Mason City YMCA |
| Masonic Opera House |
| Masonic Temple |
| 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 |
| Maynard Town Hall and Jail |
| Maysville Schoolhouse |
| 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's General Store |
| McClung, J. J., House |
| McColl, Anthony M., House |
| McCollister, James, Farmstead |
| McConn, Daniel, Barn |
| McCormick Harvesting Machine Company Building |
| McCoy Polygonal Barn |
| McDonald House |
| McElhinny House |
| McGee School |
| McGreer, John, Barn and Crib |
| McHaffey Opera House |
| McHarg, Joseph S., House |
| McHenry, William A., House |
| McKee Button Company |
| McKenzie, Erza, Round Barn |
| 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 |
| McQuilkin, James Greer, Round Barn |
| McWaid, Job A. and Rebecca E., House |
| Meadly House |
| Mears Hall |
| Meek's Flour Mill |
| Meier, Fred W., Round Barn |
| Meiser Drug Store |
| Melcher, Dennis Melcher, Pottery and House |
| Mellinger Memorial Library |
| Memorial Building |
| Mentzer, Joseph P., House |
| Merchants' National Bank |
| Merrero Building |
| Methodist Deaconess Institute-Esther Hall |
| Metropolitan Opera House |
| Metz Manufacturing Company |
| Middlefork Methodist Episcopal Church |
| Middleton, Dr. George McLelland, House and Garage |
| Miller, Alvin, House |
| Miller Building |
| Miller, F. H., House |
| Miller, Justice Samuel Freeman, House |
| Miller, Norris, House |
| Miller Round Barn |
| Miller, Severin, House |
| Mill Rock School |
| Milwaukee and St. Paul Railway Combination Depot |
| Minburn Railroad Depot |
| Missouri, Iowa & Nebraska Railway Co. Depot-Weldon |
| Mitchell County Courthouse |
| Mitchell-Maskrey Mill |
| Modale School and Masonic Hall |
| Moeszinger-Marquis Hardware Co. |
| Monona County Courthouse |
| Monroe County Courthouse |
| Montauk |
| Montgomery County Courthouse |
| Montgomery County Jail |
| Moorehead Stagecoach Inn |
| Moore, Josiah B. and Sara, House |
Data from United States Park Service and Wikidata
