Ohio - Significance region: Local
| Linneman Building |
| Lion Knitting Mills |
| Liquid Carbonic Corporation Dry Ice Plant |
| Lisbon Historic District |
| Livingston, Alexander W., House |
| Lloyd, John Uri, House |
| Lockwood, J. C., House |
| Loew-Define Grocery Store and Home |
| Logan City Hall |
| Logan Historic District |
| London Commercial Business Historic District |
| Long and Third Commercial Building |
| Longenecker, Doctor, Office Building |
| Long-Mueller House |
| Long-Romspert House |
| Look About Lodge |
| Lorain Avenue Commercial Historic District |
| Lorain Carnegie Public Library |
| Lorain Fire Station No. 1 |
| Lorain Lighthouse |
| Lorain Station Historic District |
| Lorain YMCA Building |
| Lord, Addison, House |
| Lost Lane Farm |
| Lotz, Henry, Stone |
| Louisville Historic District |
| Loveridge, Richard and Ann, House |
| Lowellville Railroad Station |
| Lower Price Hill Historic District |
| Lower Prospect-Huron Historic District |
| Lowrie, S. Gale and Agnes P., House |
| Lubal Manufacturing and Distributing Company, The |
| Lucas County Hospital and Nurse's Home |
| Ludowici Roof Tile Company Historic District |
| Ludwig, Isaac R., Historical Mill |
| Luethstrom-Hurin House |
| LuNeack House |
| Lunkenheimer, Frederick, House |
| Luthor List Mound |
| Lutz-Martin Farm |
| Lutz's Tavern |
| Lyle, Samuel, Log House |
| Lyman, William, House |
| Lynnwood Farm |
| MacDonell House |
| Macedonia Church |
| Mace, Henry, House |
| Mackinaw Historic District |
| Macksville Tavern |
| MacNichol Site |
| Macomb, Mary Worthington, House |
| Madam Fredin's Eden Park School and Neighboring Row House |
| Madeira Railroad Depot |
| Madison and Woodburn Historic District |
| Madison Avenue Historic District |
| Madison Seminary And Home |
| Madison-Stewart Historic District |
| Mad River Block |
| Magnolia-Wade Park Historic District |
| 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 Theatre |
| Main-Third Street Buildings |
| Malio House |
| Mallory, Ogden, House |
| Maltby, Henry, House |
| Mann Mound |
| Manse Hotel and Manse Hotel Annex |
| Mansfield, Judge, House |
| Mansfield Savings Bank |
| Mansfield Woman's Club |
| Mantua Center School |
| Mantua Station Brick Commercial District |
| Maplewood |
| March, George, House |
| March, George, House |
| Mardot Antique Shop |
| Mariemont Embankment And Village Site |
| Marion Catholic School |
| Marion Cemetery Receiving Vault |
| Marion County Courthouse |
| Marion County Telephone Company Building |
| Marion Downtown Historic District |
| Marion Township School District No. 3 |
| Marion Township Sub-District #8 School |
| Marion Women's Club Home |
| Market-Mohawk Center |
| Market Square |
| Market Street Section, Retaining Wall and Water Trough |
| Markham Mound |
| Mark Road Bridge |
| Marks-Family House |
Data from United States Park Service and Wikidata
