Connecticut - Significance region: Local
| Kelsey, Ezekiel, House |
| Kendrick, John, House |
| Keney Tower |
| Kensington Grammar School-Jean E. Hooker High School |
| Kent Iron Furnace |
| Killingly High School, Old |
| King, Alexander, House |
| King, George, House |
| Knap, John, House |
| Knapp Tavern |
| Knesseth Israel Synagogue |
| Kraus Corset Factory |
| Lambert, David, House |
| Lamb Homestead |
| Lathrop, Dr. Daniel, School |
| Lathrop, Dr. Joshua, House |
| Lathrop-Mathewson-Ross House |
| Lattin, Nathan B., Farm |
| Laurel Beach Casino |
| Lay-Pritchett House |
| Lee, Daniel and Mary, House |
| Leete, Pelatiah, House |
| Le Roy Shirt Company Factory |
| Lester, Nathan, House |
| Lester, Timothy, Farmstead |
| Lewis, Isaac, House |
| Lewis Street Block |
| Lewis-Zukowski House |
| Lighthouse Inn |
| Linden Apartments |
| Little Bethel African Methodist Episcopal Church |
| Little Plain Historic District |
| Locust Avenue School |
| Long Society Meetinghouse |
| Loomis-Pomeroy House |
| Lord, Capt. Enoch, House |
| Loth, Joseph, Company Building |
| Lyman, David, II, House |
| Lyman House |
| Lyman, Thomas, House |
| Lyon, Thomas, House |
| Main Sawmill |
| Main Street Bridge |
| Mallett, David, Jr., House |
| Mansfield Hollow Dam |
| Mansfield, Richard, House |
| Mansuy and Smith Automobile Showroom Building |
| Maplewood School |
| Marlborough House |
| Martin, Caleb, House |
| Marvin Tavern |
| Masonic Temple |
| Mather Homestead |
| Matthews and Willard Factory |
| Meadowlands |
| Memorial Hall |
| Meriden Curtain Fixture Company Factory |
| Merritt Beach & Son Building |
| Merryall Union Evangelical Society Chapel |
| Methodist Episcopal Church |
| Middle Haddam School |
| Middletown South Green Historic District |
| Miller, Henry F., House |
| Mills, Elijah, House |
| Mills, Oliver W., House |
| Minterburn Mill |
| Moody, Dr. Mary B., House |
| Moore Jr., William, House |
| Moore, Roswell, II, House |
| Morris Cove Historic District |
| Morris House |
| Mount Carmel Congregational Church and Parish House |
| Mount St. Joseph Academy |
| Mystic Bank |
| Nathaniel Witherell Historic District |
| Neiditz Building |
| New Britain Opera House |
| New Britain Public High School Campus |
| New Haven Armory |
| New London County Courthouse |
| New London Public Library |
| New Mill and Depot Building, Hawthorne Woolen Mill |
| Nichols, George Pickering, House |
| Nicoll, Caroline, House |
| Norcross Brothers Granite Quarry |
| Northfield Knife Company Site |
| Northford Center |
| North-West School |
| Noyes, William, Farmstead |
| O'Connell, Clara T., School |
| Octagon House |
| Ogden, David, House |
| Ohev Sholem Synagogue |
| Oil Mill Historic District |
| Old Farm Schoolhouse |
| Old Lyme Historic District |
| Old Middletown High School |
| Old North Cemetery |
| Old Riverton Inn |
| Old Rockville High School and East School |
Data from United States Park Service and Wikidata
