Connecticut - Criteria: C (architecture/engineering)
| Moore, Roswell, II, House |
| Morris House |
| Mory's |
| Moseley House-Farm |
| Moss Hill |
| Mount Carmel Congregational Church and Parish House |
| Mount St. Joseph Academy |
| Mount Tom Tower |
| Mulville House |
| Municipal Building |
| Murphy, Charles and Peggy House |
| Murphy, Patrick, House |
| Murray, Jonathan, House |
| Music Mountain |
| Myers and Gross Building |
| Mystic Bank |
| Mystic Bridge Historic District |
| Mystic River Historic District |
| Natchaug Forest Lumber Shed |
| Nathaniel Wheeler Memorial Fountain |
| Nathaniel Witherell Historic District |
| National Hall Historic District |
| Naubuc Avenue-Broad Street Historic District |
| Naugatuck Center Historic District |
| Nehemiah Royce House |
| New Britain Public High School Campus |
| New Haven City Hall |
| New Haven Clock Company Factory |
| New Haven County Courthouse |
| New Haven District Campground |
| New Haven Green Historic District |
| New Haven Jewish Home for the Aged |
| New Haven Lawn Club |
| New Haven Railroad Danbury Turntable |
| New Haven Railroad Station |
| Newington Junction Railroad Depot |
| Newington Junction South Historic District |
| New London County Courthouse |
| New London Customhouse |
| New London Harbor Lighthouse |
| New London Ledge Lighthouse |
| New London Public Library |
| New London Railroad Station |
| New Milford Center Historic District |
| New Mill and Depot Building, Hawthorne Woolen Mill |
| New Preston Hill Historic District |
| Newtown Borough Historic District |
| New York Belting and Packing Co. |
| Nichols Farms Historic District |
| Nichols, George Pickering, House |
| Nicoll, Caroline, House |
| Ninth Square Historic District |
| Noank Historic District |
| Noble House |
| Noble, John Glover, House |
| Nook Farm and Woodland Street District |
| Norfield Historic District |
| Norfolk Country Club House |
| Norfolk Downs Shelter |
| Norfolk Historic District |
| Northam Memorial Chapel and Gallup Memorial Gateway |
| North Branford Center Historic District |
| North Cove Historic District |
| Northford Center |
| North Grosvenordale Mill Historic Disrict |
| North Stonington Village Historic District |
| North-West School |
| Norton House |
| Norwalk City Hall |
| Norwalk Green Historic District |
| Norwalk Island Lighthouse |
| Norwalk River Railroad Bridge |
| Norwich Hospital District |
| Norwich Town Hall |
| Norwichtown Historic District |
| Noyes House |
| Noyes, William, Farmstead |
| Oak Lodge |
| Occum Hydroelectric Plant and Dam |
| O'Connell, Clara T., School |
| Octagon House |
| Octagon House |
| Ogden, David, House |
| Ohev Sholem Synagogue |
| Old Farm Schoolhouse |
| Old Lyme Historic District |
| Old Middletown High School |
| Old North Cemetery |
| Old Rockville High School and East School |
| Old Saybrook South Green |
| Old Saybrook Town Hall and Theater |
| Old Town Hall |
| Old Town Hall |
| Old Westfield Cemetery |
| Old West Haven High School |
| Old Wethersfield Historic District |
| Oliver White Tavern |
| Orange Center Historic District |
| Orange Street Historic District |
| Osbornedale |
Data from United States Park Service and Wikidata
