Connecticut - Criteria: C (architecture/engineering)
| Smith, Samuel, House |
| Smith, Shubel, House |
| Somers Historic District |
| Somersville Historic District |
| Sound Beach Railroad Station |
| South Britain Historic District |
| Southbury Historic District No. 1 |
| Southbury Training School |
| South Canaan Congregational Church |
| South Congregational Church |
| South Coventry Historic District |
| South End Historic District |
| South End Historic District |
| Southern New England Telephone Company Adminstrative Building |
| Southern New England Telephone Company Building |
| Southington Center Historic District |
| Southington Public Library |
| South Main and Washington Streets Historic District |
| Southport Historic District |
| South School |
| Southwest District School |
| Southwest District School |
| Southwest Ledge Lighthouse |
| South Willington Historic District |
| Spanish House, The |
| Spencer House |
| Sports Building |
| Sprague, Elias, House |
| Springbank |
| Spring Grove Cemetery |
| Stackpole, Moore, and Tryon Building |
| Stafford Hollow Historic District |
| Stamford Harbor Lighthouse |
| St. Andrew's Episcopal Church |
| St. Andrew's Protestant Episcopal Church |
| Stanley-Whitman House |
| Stanley-Woodruff-Allen House |
| Stanton, Robert, House |
| Stapleton Building |
| Starr, C. J., Barn and Carriage House |
| Starr Mill |
| Starr Mill Road Bridge |
| State Arsenal and Armory |
| State Park Supply Yard |
| St. Benedict's Church |
| Steamboat Dock Site |
| Steele, Allyn, House |
| Sterling Block-Bishop Arcade |
| Sterling Hill Historic District |
| Sterling Hill Historic District |
| Sterling Homestead |
| Stevenson Dam Hydroelectric Plant |
| Stevens, William, House |
| Stick Style House at Stony Creek |
| St. James' Episcopal Church |
| St. John's Episcopal Church |
| St. John's Episcopal Church |
| St. John's Episcopal Church |
| St. John's Protestant Episcopal Church |
| St. Luke's Chapel |
| St. Luke's Episcopal Church |
| St. Mary's Church |
| St. Mary's Parochial School |
| Stoddard, Capt. Mark, Farmstead |
| Stoeckel, Robbins, House |
| Stone Bridge |
| Stone, Medad, Tavern |
| Stonington Cemetery |
| Stonington Harbor Lighthouse |
| Stonington High School |
| Stony Creek-Thimble Islands Historic District |
| Stony Hill School |
| St. Paul's Methodist Episcopal Church |
| St. Peter's Episcopal Church |
| Stratfield Historic District |
| Stratford Center Historic District |
| Stratford Point Lighthouse |
| Stratford Shoal Lighthouse |
| Strickland Road Historic District |
| Strong House |
| Strouse, Adler Company Corset Factory |
| Sts. Cyril and Methodius Church |
| Sturges, Jonathan, House |
| Sturges-Wright House |
| Suburban Club |
| Suffield Historic District |
| Sumner-Carpenter House |
| Sunny Ridge Historic District |
| Sun Terrace |
| Swain-Harrison House |
| Swallen, James, House |
| Sweetland, Sophia, House |
| Swift, M. and Sons Company |
| System House |
| Taftville |
| Talcottville Historic District |
| Tamarack Lodge Bungalow |
| Tariffville Historic District |
| Tarrywile |
| Tatum, Corinne and George Liston Jr., House |
Data from United States Park Service and Wikidata
