Connecticut - Criteria: A (event)
| Kent Iron Furnace |
| Kettle Creek Historic District |
| Killingly High School, Old |
| King, George, House |
| Kings Highway North Historic District |
| Kinne Cemetery |
| Knowlton Memorial Hall |
| Kraus Corset Factory |
| L. A. DUNTON |
| Lake Compounce Carousel |
| Lakeville Historic District |
| Lakeville Manor |
| Lambert, David, House |
| Lamb Homestead |
| Lathrop, Dr. Daniel, School |
| Laurel Beach Casino |
| Laurel Hill Historic District |
| Lawrence, Isaac, House |
| Lawton Mills Historic District |
| Lebanon Green Historic District |
| Lee, John Black, House I |
| Le Roy Shirt Company Factory |
| Lester, Timothy, Farmstead |
| Lewis-Zukowski House |
| Lighthouse Inn |
| Lighthouse Point Carousel |
| Lime Rock Historic District |
| Lime Rock Park Race Track |
| Lincoln Theatre |
| Little Bethel African Methodist Episcopal Church |
| Little Haddam Historic District |
| Little Hollywood Historic District |
| Little Plain Historic District |
| Locust Avenue School |
| Long Ridge Village Historic District |
| Long Society Meetinghouse |
| Loomis, Capt. James, House |
| Loomis, Col. James, House |
| Loomis, George G., House |
| Loomis, Gordon, House |
| Loomis, Ira, Jr., House |
| Lord, Capt. Enoch, House |
| Loth, Joseph, Company Building |
| Lover's Leap Bridge |
| Lyman Viaduct |
| Lynde Point Lighthouse |
| Lyon, Thomas, House |
| Madison Green Historic District |
| Magill, Henry, House |
| Main Sawmill |
| Main Street Bridge |
| Main Street Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Main Street Historic District |
| Main Street Historic District No. 2 |
| Mallett, David, Jr., House |
| Maltby-Stevens Factory Site |
| Manchester Historic District |
| Mansfield Center Cemetery |
| Mansfield Hollow Dam |
| Mansfield Hollow Historic District |
| Mansfield Training School and Hospital |
| Mansuy and Smith Automobile Showroom Building |
| Maplewood School |
| Marlborough Congregational Church |
| Marlborough Street Historic District |
| Marlborough Tavern |
| Martin, Caleb, House |
| Massacoe Forest Pavilion |
| Mather Homestead |
| Mechanic Street Historic District |
| Meeker's Hardware |
| Meeting House Hill Historic District |
| Melrose |
| Melrose Road Bridge |
| Memorial Hall |
| Meriden Avenue-Oakland Road Historic District |
| Meriden Curtain Fixture Company Factory |
| Merritt Beach & Son Building |
| Merritt Parkway |
| Merwinsville Hotel |
| Metropolitan African Methodist Episcopal Zion Church |
| Metro South Historic District |
| Mianus River Railroad Bridge |
| Middlebury Center Historic District |
| Middle Haddam Historic District |
| Middletown Alms House |
| Middletown Upper Houses Historic District |
| Milford Point Hotel |
| Mill Cove Historic District |
| Millington Green Historic District |
| Mills, Beaven W., House |
| Mills, Oliver W., House |
| Mills, Timothy Dwight, House |
| Mills, Willis N, House |
| Milton Center Historic District |
| Minortown Road Bridge |
| Minterburn Mill |
Data from United States Park Service and Wikidata
