Ohio - Area of significance: Commerce
| Ludwig, Isaac R., Historical Mill |
| Macksville Tavern |
| Macomb, Mary Worthington, House |
| Madison Avenue Historic District |
| Mahoning National Bank Building |
| Main Exchange Historic District |
| Main-Market Historic District |
| Main Street Commercial Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Mantua Station Brick Commercial District |
| Marblehead Lighthouse |
| Marietta Historic District |
| Marion Downtown Historic District |
| Marlow Theatre |
| Massillon Downtown Historic District |
| Maumee Sidecut |
| Maumee Uptown Historic District |
| May Company |
| McCarthy-Blosser-Dillon Building |
| McClure-Nesbitt Motor Company |
| McConnelsville Historic District |
| McCormick Manufacturing Company Building |
| McCrory Building |
| McKelvey-Higbee Co. Buildings |
| Mead House |
| Mechanicsburg Commercial Historic District |
| Medina Farmers Exchange Co. |
| Medina Public Square Historic District |
| Meek, J.F., Buildings |
| Merriman, Wells E., House |
| Metropolitan Block |
| Miami And Erie Canal, Deep Cut |
| Miami-Erie Canal Lock No. 70 |
| Miami-Erie Canal Site Historic District |
| Milan Historic District |
| Mill & Dunn Historic District |
| Millersburg Historic District |
| Miner's Supply Store |
| Mooney, William C., House |
| Moore, Leonard M., House |
| Morristown Historic District |
| Morrow-Overman-Fairley House |
| Mott Drug Store |
| Mount Victory Historic District |
| Municipal Building |
| Myers Block-Home Company Building |
| Myers Daily Market |
| Nafzger-Miller House |
| Nelsonville Historic District |
| Newark Downtown Historic District |
| New Baltimore Inn |
| New England Building |
| North Columbus Commercial Historic District |
| North End Neighborhood Historic District |
| Northern Ohio Blanket Mills |
| North High Street Historic District |
| North Main-North Detroit Street Historic District |
| North Market Historic District |
| North Union Shaker Site |
| Oesterlein Machine Company-Fashion Frocks, Inc. Complex |
| Ohio and Erie Canal |
| Ohio Bell Henderson-Endicott Exchange Building |
| Ohio Farm Bureau Federation Offices |
| Ohio Finance Building |
| Ohio Moline Plow Company Building |
| Old Harbour Store |
| Old Hotel, The |
| Old Mill |
| Old River Road Historic District |
| Old Tippecanoe Main Street Historic District |
| Old Vermilion Mill |
| O'Neil's Department Store |
| Onesto Hotel |
| O. P. Boyer’s and Sons Funeral Home |
| Oregon Historic District |
| Orrville Downtown Historic District |
| Our House |
| Outville Hay and Grain Company Building |
| Overfield Tavern |
| Over-the-Rhine Historic District |
| Oxford Railroad Depot and Junction House |
| Paige, David R., House |
| Palmyra Center Hotel |
| Paulding Downtown Historic District |
| Peeble's Corner Historic District |
| Peggy Ann Building |
| Peninsula Village Historic District |
| Pennsylvania Depot |
| Perrysburg Historic District |
| Phoenix Mills |
| Plymouth Historic District |
| Pomeroy Historic District |
| Potters National Bank |
| Potters Savings and Loan |
| Procter and Collier-Beau Brummell Building |
| Prospect Place |
| Providence Historic District |
| Provident Savings Bank and Trust Co. |
Data from United States Park Service and Wikidata
