Iowa - Criteria: C (architecture/engineering)
| Snowden House |
| Sokol Gymnasium |
| South Summit Street District |
| Southwest Fifth St. Bridge |
| Spencer, Charles H., House |
| Spencer, Roswell, House |
| Spirit Lake Public Library |
| Spotts Round Barn |
| Sprague, Brown, and Knowlton Store |
| Springbrook State Park, Civilian Conservation Corps Area |
| Spring Creek Friends Cemetery |
| Spring Creek Meeting House-H Street Mission |
| Spring Side |
| Squaw Creek Bridge 2 |
| Squiers, J. E., House |
| Squirrel Hollow County Park Historic District |
| St. Ambrose Cathedral and Rectory |
| Star-Clipper-Canfield Building and Winding Stairway |
| Starker-Leopold Historic District |
| State Bank of Stratford |
| State Center Commercial Historic District |
| State Quarry, Iowa Men's Reformatory |
| State Savings Bank |
| State Savings Bank |
| State Savings Bank |
| State Street Bridge |
| Stauer, Peter, House |
| St. Boniface Historic District |
| St. Boniface of New Vienna Historic District |
| Steamboat Rock Consolidated Schools Building |
| Stearns, C. S., House |
| Stemmer, J. C., House |
| Stephens, A. J., House |
| Stevenson, Samuel A. and Margaret, House |
| Stewart Avenue Bridge |
| Stewart, Frank, House |
| Stewart, J. W., House |
| Stewart Library |
| Steyer Bridge |
| Steyer Opera House |
| St. James Episcopal Church |
| St. James United Methodist Church |
| St. John's Episcopal Church and Parish Hall |
| St. John's Methodist Episcopal Church |
| St. Joseph Church and Parish Hall |
| St. Joseph Hospital Historic District |
| St. Joseph's Catholic Church |
| St. Joseph's Roman Catholic Church |
| St. Joseph's Roman Catholic Church and Cemetery Historic District |
| St. Katherine's Historic District |
| St. Lawrence Catholic Church |
| St. Luke's Methodist Church |
| St. Luke's Methodist Episcopal Church |
| St. Luke's School and Recreation Center |
| St Mary of the Assumption Church |
| St. Mary's Academy |
| St. Mary's Catholic Church Historic District |
| St. Mary's Catholic Church Historic District |
| St. Mary's Church and Rectory |
| St. Mary's Parish Church Buildings |
| St. Mary's Rectory |
| St. Mary's Roman Catholic Church Complex |
| St. Matthew's by the Bridge Episcopal Church |
| St. Michael's Church, Cemetery, Rectory and Ancient Order of Hibernians Hall |
| Stock Judging Pavilion |
| Stockman, Dr. G. C., House |
| Stoe Creek Bridge |
| St. Olaf Auditorium |
| Stone Academy |
| Stone Barn |
| Stone City Historic District |
| Stone House |
| Stoner, Thomas I., House |
| Stone School |
| Storm Creek Bridge |
| Storm Creek Bridge 2 |
| Storm Lake High School |
| Storm Lake Public Library |
| St. Patrick Church |
| St. Patrick's Catholic Church, Cedar |
| St. Patrick's Church-Garryowen |
| St. Paul Methodist Episcopal Church |
| St. Paul's English Lutheran Church |
| St. Paul's Episcopal Church |
| St. Paul's Episcopal Church |
| St. Paul's Episcopal Church and Parish Hall |
| St. Peter Church |
| St. Peter's Church and Rectory |
| St. Peters United Evangelical Lutheran Church |
| Stranahan, Prof. Edgar H. and Irene D., House |
| Stratton House |
| Stringtown House |
| Struck, Dr. Kuno, House |
| St. Stephen's Episcopal Church |
| St. Thomas Episcopal Church |
| Stubbins, George E., House |
| Stuckslager, Harrison, House |
| Studebaker Corporation Branch Office Building |
| Sturdevant Southwest Historic District |
| Sturdivant-Sawyer House |
Data from United States Park Service and Wikidata
