| Abington Congregational Church | Abington | Building | 1977 |
| Aldrich Free Public Library | Plainfield | Building | 1994 |
| American Thread Company | Willimantic | District | 2014 |
| Ashford Academy | Ashford | Building | 1988 |
| Bosworth, Benjamin, House | Eastford | Building | 1978 |
| Bowen, Henry C., House NHL | Woodstock | Building | 1977 |
| Bowen, Mathew, Homestead | Woodstock | Building | 1987 |
| Brayton Grist Mill | Pomfret | Building | 1986 |
| Broad Street-Davis Park Historic District | Killingly | District | 1998 |
| Brooklyn Green Historic District | Brooklyn | District | 1982 |
| Bush Hill Historic District | Brooklyn | District | 1987 |
| Butts Bridge | Canterbury | Structure | 2010 |
| Cady-Copp House | Putnam | Building | 2001 |
| Canterbury Center Historic District | Canterbury | District | 1998 |
| Cargill Falls Mill (Wilkinson Mill) | Putnam | District | 2014 |
| Central Village Historic District | Plainfield | District | 1991 |
| Chandler, Capt. Seth, House | East Woodstock | Building | 1993 |
| Chaplin Historic District | Chaplin | District | 1978 |
| Church Farm | Ashford | Building | 1988 |
| Clark, Capt. John, House | Canterbury | Building | 1970 |
| Crandall, Prudence, House NHL | Canterbury | Building | 1970 |
| Daniel's Village Archeological Site | Killingly | Site | 1978 |
| Danielson Main Street Historic District | Killingly | District | 1992 |
| Dayville Historic District | Killingly | District | 1988 |
| Dorrance Inn | Sterling | Building | 2002 |
| Elliottville Lower Mill | East Killingly | Building | 1982 |
| First Congregational Church of Plainfield | Plainfield | Building | 1986 |
| Forty-Seventh Camp of Rochambeau's Army | Windham | Site | 2003 |
| Fourth Camp of Rochambeau's Army | Windham | Site | 2003 |
| Glen Falls Bridge | Plainfield | Structure | 1999 |
| Gwyn Careg | Abington | Building | 1994 |
| Hampton Hill Historic District | Hampton | District | 1982 |
| Hemlock Glen Industrial Archeological District | Hampton | District | 2007 |
| Hunt, Dr. Chester, Office | Windham Center | Building | 1970 |
| Huntington, Samuel, Birthplace NHL | Scotland | Building | 1971 |
| Isaac and Sarah Upham House | Thompson | Building | 2025 |
| Israel Putnam School | Putnam | Building | 1984 |
| Jillson, William, Stone House | Willimantic | Building | 1971 |
| Killingly High School, Old | Killingly | Building | 1992 |
| Knowlton Memorial Hall | Ashford | Building | 1994 |
| Lawton Mills Historic District | Plainfield | District | 1996 |
| Main Street Historic District | Willimantic | District | 1982 |
| Main Street Historic District (Boundary Increase) | Windham | District | 1992 |
| March Route of Rochambeau's Army: Manship Road-Barstow Road | Canterbury | District | 2003 |
| March Route of Rochambeau's Army: Old Canterbury Road | Plainfield | District | 2003 |
| March Route of Rochambeau's Army: Palmer Road | Scotland | District | 2003 |
| March Route of Rochambeau's Army: Plainfield Pike | Plainfield | District | 2003 |
| March Route of Rochambeau's Army: Scotland Road | Windham | District | 2003 |
| Mixer Tavern | Ashford | Building | 1994 |
| Natchaug Forest Lumber Shed | Eastford | Building | 1986 |
| New Roxbury Ironworks Site | Woodstock | Site | 1996 |
| Nichols, George Pickering, House | Thompson | Building | 1991 |
| North Grosvenordale Mill Historic Disrict | Thompson | District | 1993 |
| Old Westfield Cemetery | Killingly | Site | 2010 |
| Packerville Bridge | Plainfield | Structure | 1992 |
| Plainfield Street Historic District | Plainfield | District | 1991 |
| Plainfield Woolen Company Mill | Plainfield | Building | 1985 |
| Pomfret Street Historic District | Pomfret | District | 1998 |
| Pomfret Town House | Pomfret | Building | 1989 |
| Prospect Hill Historic District | Willimatic | District | 2003 |
| Putnam Farm | Brooklyn | Building | 1982 |
| Putnam High School | Putnam | Building | 1993 |
| Putnam Railroad Station | Putnam | Building | 2007 |
| Putnam, Israel, Wolf Den | Pomfret | Site | 1985 |
| Quinebaug Mill-Quebec Square Historic District | Brookland-Killingly | District | 1985 |
| Quinebaug River Prehistoric Archeological District | Canterbury | District | 2009 |
| Ramsdell, Hezekiah S., Farm Site | Thompson | Building | 1990 |
| Sterling Hill Historic District | Sterling | District | 1986 |
| Sumner-Carpenter House | Eastford | Building | 1991 |
| Taylor's Corner | Woodstock | Building | 1989 |
| Temple Beth Israel | Danielson | Building | 2013 |
| Thompson Hill Historic District | Thompson | District | 1987 |
| Trinity Church | Brooklyn | Building | 1970 |
| Union Society of Phoenixville House | Eastford | Building | 2007 |
| Unitarian Meetinghouse | Brooklyn | Building | 1972 |
| Wauregan Historic District | Plainfield | District | 1979 |
| Wheeler, Jonathan, House | Canterbury | Building | 1982 |
| Willimantic Armory | Windham | Building | 1985 |
| Willimantic Elks Club | Windham | Building | 2005 |
| Willimantic Footbridge | Willimantic | Structure | 1979 |
| Willimantic Freight House and Office | Willimantic | Building | 1982 |
| Windham Center Historic District | Windham | District | 1979 |
| Witter House | Chaplin | Building | 1970 |
| Woodstock Academy Classroom Building | Woodstock | Building | 1984 |
| Woodstock Hill Historic District | Woodstock | District | 1999 |
| Wylie School | Voluntown | Building | 1991 |