Connecticut - Criteria: C (architecture/engineering)
| House at 736 Palisado Avenue |
| House at 847 Main Street, North |
| Howard Avenue Historic District |
| Howd, Eliphalet, House |
| Howd-Linsley House |
| Howe, John I., House |
| Hoyt-Barnum House |
| Hoyt-Burwell-Morse House |
| Hubbard, Nehemiah, House |
| Hubbard Park |
| Humphrey, John, House |
| Humphreys, Gen. David, House |
| Huntington Center Historic District |
| Huntington, Col. Joshua, House |
| Huntington, Gen. Jedidiah, House |
| Huntington Street Baptist Church |
| Hurd, William, House |
| Hurlbutt Street School |
| Hurley Road Historic District |
| Hurwood Company |
| Hyatt, Thomas, House |
| Hyde-St. John House |
| Hyland-Wildman House |
| Imlay and Laurel Streets District |
| Imperial Granum-Joseph Parker Buildings |
| Indian Harbor Yacht Club |
| Indian Hill Avenue Historic District |
| Isham-Terry House |
| Israel Putnam School |
| Ives-Baldwin House |
| Ives, Charles, House |
| Ivoryton Historic District |
| Jail Hill Historic District |
| James Pratt Funeral Service |
| Jefferson-Seymour District |
| Jerome, William I, House |
| Jillson, William, Stone House |
| Johnson, Alphonso, House |
| Johnson, Franklin, House |
| Johnson, Philip, Glass House |
| Johnson, Wilfred X., House |
| Jones, Theophilus, House |
| Jordan Village Historic District |
| Judd and Root Building |
| Judson, Capt. David, House |
| June, Lewis, House |
| Keeler Tavern |
| Kellogg, Enos, House |
| Kellogg, Gen. Martin, House |
| Kelsey, Enoch, House |
| Kelsey, Ezekiel, House |
| Kendrick, John, House |
| Keney Tower |
| Kensington Soldier's Monument |
| Kettle Creek Historic District |
| Killingly High School, Old |
| King, Alexander, House |
| King, George, House |
| King's Field House |
| Kings Highway North Historic District |
| Kinne Cemetery |
| Knap, John, House |
| Knesseth Israel Synagogue |
| Knowlton Memorial Hall |
| Kraus Corset Factory |
| L. A. DUNTON |
| Lake Compounce Carousel |
| Lakeville Historic District |
| Lambert, David, House |
| Lamb Homestead |
| Lathrop, Dr. Joshua, House |
| Lathrop-Mathewson-Ross House |
| Lattin, Nathan B., Farm |
| Laurel and Marshall Streets District |
| Laurel Hill Historic District |
| Lawrence, Isaac, House |
| Lawton Mills Historic District |
| Lay-Pritchett House |
| Lebanon Green Historic District |
| Lee, Daniel and Mary, House |
| Lee, John Black, House I |
| Leete, Pelatiah, House |
| Lee, Thomas, House |
| Leffingwell Inn |
| Le Roy Shirt Company Factory |
| Lester, Nathan, House |
| Lester, Timothy, Farmstead |
| Lewis, Isaac C., Cottage |
| Lewis, Isaac, House |
| Lewis Street Block |
| Lewis-Zukowski House |
| Lighthouse Inn |
| Lighthouse Point Carousel |
| Lime Rock Historic District |
| Lime Rock Park Race Track |
| Lincoln Theatre |
| Linden Apartments |
| Linke, William L., House |
| Litchfield Historic District |
| Litchfield-South Roads Historic District |
Data from United States Park Service and Wikidata
