Ohio - Criteria: C (architecture/engineering)
| Myers Daily Market |
| Myers Hall |
| National Home, Daughters of America |
| National Road |
| National Town and Country Club |
| Neal Clothing |
| Near Northside Historic District |
| Neely-Sieber House |
| Neff, Conrad, House |
| Neff, Edward E., House |
| Nela Park |
| Nelson, Luman, House |
| Neukom, Albert, House |
| Newark High School |
| New Baltimore Inn |
| Newberry Township School |
| New England Building |
| New Hayden Building |
| New Lyme Town Hall |
| Newman, William, House |
| New Market Township Community House |
| New Straitsville School |
| Newton Falls Covered Bridge |
| Newton, Judge Eben, House |
| Nichols, John H., House |
| Nicholson, James, House |
| Nichols, Walter, House |
| Nickel, Old, Plate Railroad Depot |
| Niles Masonic Temple |
| Nimocks House |
| Ninchelser, Dr., House |
| Ninth Street Historic District |
| No. 5 Fire Station |
| Noble County Jail and Sheriff's Office |
| Noble, Jonathan, House |
| Noble, Lewis, House |
| Nooney, William , House |
| Norfolk And Western Railroad Depot |
| Normandy Farms |
| North Bass School |
| North Columbus Commercial Historic District |
| North High School |
| North Main-North Detroit Street Historic District |
| North Market Historic District |
| North Presbyterian Church |
| North Ridgeville City Hall |
| Northrop, Julia Carter, House |
| Northside United Methodist Church |
| Norwalk Memorial Hospital |
| Norwell Residence |
| Norwood Municipal Building |
| Notre Dame Academy |
| Notre Dame College of Ohio |
| Nutwood Place |
| Oak Hill |
| Oak Hill Cottage |
| Oak Hill Welsh Congregational Church |
| Oakland Cemetery Chapel and Superintendent's House and Office |
| Oakwood |
| Oberlin Gas Lighting Company Gasholder House |
| Oberlin Lake Shore And Michigan Southern Station |
| Observatory Historic District |
| Octagon, The |
| Odd Fellows Hall |
| Odd Fellows Hall |
| Odd Fellows' Home for Orphans, Indigent and Aged |
| Odd Fellows Temple |
| Ohio Bell Henderson-Endicott Exchange Building |
| Ohio City Preservation District |
| Ohio Farm Bureau Federation Offices |
| Ohio Hospital For Epileptics Stone Water Towers |
| Ohio Institution for the Education of the Deaf and Dumb |
| Ohio Lantern Company |
| Ohio Moline Plow Company Building |
| Ohio National Bank |
| Ohio National Guard Armory |
| Ohio One-Ohio Edison |
| Ohio Power Company |
| Ohio Soldiers' And Sailors' Home |
| Ohio Stadium |
| Ohio Statehouse |
| Ohio State Normal College At Kent |
| Ohio State Reformatory |
| Ohio Theatre |
| Ohio Theatre |
| Ohio Theatre |
| Ohio Theatre |
| Ohio University Campus Green Historic District |
| Ohio Wesleyan University Student Observatory |
| Ohmer, Nicholas, House |
| Old Akron Post Office |
| Old Amherst Freight Depot |
| Old Bartlett and Goble Store |
| Old Beechwold Historic District |
| Old Carriage Barn |
| Old Center School |
| Old Central Post Office |
| Old College Hill Post Office |
| Old District 10 Schoolhouse |
| Old Enon Road Stone Arch Culvert |
Data from United States Park Service and Wikidata
