Ohio - Area of significance: Architecture
| Madison-Stewart Historic District |
| Mad River Block |
| Magnolia-Wade Park Historic District |
| Magruder Building |
| Mahoning Avenue Historic District |
| Mahoning County Courthouse |
| Mahoning National Bank Building |
| Main and Third Street Cluster |
| Main Building School |
| Main Exchange Historic District |
| Main-Market Historic District |
| Main Street Buildings |
| Main Street Commercial Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Main-Third Street Buildings |
| Malio House |
| Mallory, Ogden, House |
| Maltby, Henry, House |
| Mansfield, Judge, House |
| Mansfield Savings Bank |
| Mansfield Woman's Club |
| Mantua Center District |
| Mantua Center School |
| Mantua Station Brick Commercial District |
| Maplewood |
| March, George, House |
| Mardot Antique Shop |
| Maria Stein Catholic Church and Rectory |
| Marietta Historic District |
| Marion Catholic School |
| Marion Cemetery Receiving Vault |
| Marion County Courthouse |
| Marion Downtown Historic District |
| Marion Township School District No. 3 |
| Marion Township Sub-District #8 School |
| Market Square |
| Marks-Family House |
| Marlow Theatre |
| Marmon, Martin, House |
| Marquart-Mercer Farm |
| Marshall, David, House |
| Marshall, James E., House |
| Marsh, George H., Homestead and the Marsh Foundation School |
| Marsh, Joseph, House |
| Martin Block and Kibby Block |
| Martin, Brooke and Anna E. House |
| Martindale, Samuel, House |
| Marting Hotel |
| Martin House |
| Martin, Joseph, House |
| Marvin Memorial Library |
| Marysville Historic District |
| Mason, Frank H., House |
| Mason House |
| Masonic Temple |
| Masonic Temple |
| Masonic Temple |
| Masonic Temple |
| Masonic Temple |
| Masonic Temple Building |
| Masonic Temple Building |
| Mason, James, House |
| Mason, John Wesley, Gothic Cottage |
| Massillon Cemetery Building |
| Massillon Downtown Historic District |
| Mather, Flora Stone, College District |
| Mathews House |
| Mattoon-Woodrow House |
| Maudru House |
| Maumee Historic District |
| Maumee Theater |
| Maumee Uptown Historic District |
| May Company |
| May, David and Mary, House |
| Mayer, S. C., House |
| Mayfield Heights Historic District |
| May Realty Building |
| McBean, Daniel, Farmstead |
| McCafferty Run Farmstead |
| McCafferty, William, Farmhouse |
| McCarthy-Blosser-Dillon Building |
| McClelland, Harry S., House |
| McConnelsville Historic District |
| McCorkle, Almon G., House |
| McCormick Manufacturing Company Building |
| McCracken-McFarland House |
| McCracken-Scott House |
| McCracken-Sells House |
| McCrea, Matthew, House |
| McCreary-Burnworth House |
| McCrory Building |
| McCully Log House |
| McCune's Villa |
| McDannald Homestead |
| McDonald Farm |
| McDowell, Austin, House |
| McDowell, R.M. and Elizabeth, House |
| McFarland, Duncan, House |
Data from United States Park Service and Wikidata
