Iowa - Criteria: C (architecture/engineering)
| Saints Peter and Paul Roman Catholic Church Historic District |
| Salisbury House |
| Sample, Hugh W. and Sarah, House |
| Sanborn, C. M., Building |
| Sargent's Garage |
| Sauser-Lane House |
| Savanna-Sabula Bridge |
| Savery Hotel |
| Schebler, Richard, House |
| Scheibe, Julius, Cottage |
| Schindhelm-Drews House |
| Schlapp, George E., House |
| Schmidt Block |
| Schmidt, F. Jacob, House |
| Schmidt House |
| Schmidt, Louis C. and Amelia L., House |
| Schnellbacher, John and Fredericka Meyer, House |
| Schoenenberger, Nicholas, House and Barn |
| School Number 6 |
| Schramm Building |
| Schricker, John C., House |
| Schricker, John, House |
| Schroeder Bros, Meat Market |
| Schroeder-Klein Grocery Company Warehouse |
| Schrup, John and Marie (Palen) Farmstead Historic District |
| Schulein, Ben and Harriet, House |
| Schultz Brothers Drug Store |
| Science Hall |
| Sciola Missionary Baptist Church |
| Scott County Jail |
| Scottish Rite Consistory Building |
| Second and Third Avenue Historic District |
| Secrest Octagon Barn |
| Security Building |
| Security Building |
| Seeberger-Loring-Kilburn House |
| Seerley, William and Mary (Messersmith) Barn and Milkhouse-Smokehouse |
| Seminary Hill Residential Historic District |
| Seney, Charles, House |
| Sentinel Block |
| SERGEANT FLOYD |
| Seth Richards Commercial Block |
| Seven Oaks |
| Sharon Cemetery Historic District |
| Sharon, Fred B., House |
| Shaw, Col. William T. and Elizabeth C., House |
| Shaw, E. A., House |
| Shay, Lee, Farmhouse |
| Sheaffer, Craig and Virginia, House |
| Shea, John J. and Agnes, House |
| Shelby Consolidated School |
| Shelby County Courthouse |
| Sheldahl First Norwegian Evangelical Lutheran Church |
| Shellito, Dr. Judd C. and Margaret S. Clarke, House |
| Shell Rock Bridge |
| Shellsburg Bridge |
| Sherman Hill Historic District |
| Sherman, Hoyt, Place |
| Sherman Nursery Company Historic District |
| Sherrill Mount House |
| Shields Woolen Mill |
| Shipley, C. P., House |
| Shoemake, John H., House |
| Shriver, William R. and Martha Foster, House |
| Siebels' Department Store-Boyer Valley Bank |
| Sieben, Mrs. Margaret, House |
| Siemer House |
| Sigma Pi Fraternity House |
| Sigma Sigma-Delta Chi Fraternity House |
| Sigourney Public Library |
| Simmons Hardware Company Warehouse |
| Simpson, Charles S., House |
| Sinclair, Caroline, Mansion |
| Sinnett Octagon House |
| Sioux City Baptist Church |
| Sioux City Fire Station Number 3 |
| Sioux City Free Public Library |
| Sioux City Linseed Oil Works |
| Sioux City Masonic Temple |
| Sioux County Courthouse |
| Sioux Theatre |
| Sitz, Rudolph H., Building |
| Sixth and Forest Historic District |
| Skunk River Bridge |
| Slayton Farms-Round Barn |
| Slye, Thomas, House |
| Smith, Alvord I., House |
| Smith Farmhouse |
| Smith, Gen. Cass and Belle, House |
| Smith, Henry H./J.H. Murphy House |
| Smith, Hiram C., House |
| Smith, Hiram C., Milking Shed |
| Smith, James, House |
| Smith-Johnson House |
| Smith, Peter and Mary, House |
| Smith, William G., House |
| Smouse, David W., Opportunity School |
| Snake Alley |
| Snake Alley Historic District |
| Snider Bridge |
Data from United States Park Service and Wikidata
