Iowa - Criteria: C (architecture/engineering)
| Interior Telephone Company Building |
| IOOF Building |
| I.O.O.F. Hall |
| I.O.O.F. Hall |
| Iowa Building |
| Iowa Canning Company Seed House Building |
| Iowa County Courthouse |
| Iowa-Des Moines National Bank Building |
| Iowa Falls Bridge |
| Iowa Falls Union Depot |
| Iowa Lakeside Laboratory Historic District |
| Iowa Men's Reformatory Cemetery |
| Iowa Men's Reformatory Historic District |
| Iowan's Hotel |
| Iowa Soldiers' Orphans' Home |
| Iowa State Capitol |
| Iowa State Fair and Exposition Grounds Historic District |
| Iowa State Historical Building |
| Iowa Wind Mill and Pump Company Office and Warehouse |
| Iowa Yearly Meeting House-College Avenue Friends Church |
| Jackson County Courthouse |
| Jackson Park Historic District |
| Jackson-Swisher House and Carriage House |
| Jacobson Farm |
| Jagger-Churchill House |
| Janko, Jan F. and Antonie, Farmstead District |
| Jansen, Theodore, House |
| Jasper County Courthouse |
| Jay Funeral Home |
| Jefferis, Thomas, House |
| Jefferson County Courthouse |
| Jefferson Elementary School |
| Jefferson Street Historic District |
| Jefferson Street Viaduct |
| Jenkins, Dr. George A., House |
| Jewell Apartments |
| Johnson, Capt. Nicholas W. and Emma, House |
| Johnson County Courthouse |
| Johnson County Savings Bank |
| Johnson, George, House |
| Johnson, Mrs. Lydia, House |
| Johnson, Sylvanus, House |
| Johnstone, Dr. Anna E. and Andrew A., House |
| Jones Business College |
| Jones County Court House |
| Jones, G.W., Building |
| Jorgensen, Hans J., Barn |
| Joy, C. R., House |
| Julien Dubuque Bridge |
| Kahl Building |
| Kahl, Henry, House |
| Keck, Joseph, House |
| Keeler, Rev. R. W. and Fannie E., House |
| Keerl-Decker House |
| Kegler Gonner Store and Post Office |
| Keigley Branch Bridge |
| Kelley House |
| Kellogg, Miles and Elizabeth Smith, House |
| Kellow House |
| Kendall Young Public Library |
| Keokuk County Courthouse |
| Keokuk National Cemetery |
| Keokuk Union Depot |
| Keokuk Young Women's Christian Association Building |
| Kidder, Zephaniah, House |
| Kiene, Albert, House |
| Kilbourn Bridge |
| Kimball-Stevenson House |
| Kimballton Commercial District |
| Kimballton West 2nd-West 3rd Street Residential District |
| Kingman Place Historic District |
| King Memorial Chapel |
| Kinney Octagon Barn |
| Kirkpatrick, Robert Round Barn |
| Kirk, The |
| Kirkwood House |
| Kittyhawk Avenue Bridge |
| Klindt, George, House |
| Klindt, Henry, House |
| Klondike Bridge |
| Knott, Dr. Van Buren, House |
| Knoxville Veterans Administration Hospital Historic District |
| Knoxville WPA Athletic Field Historic District |
| Koch Drug Store |
| Koch, Hans M., House |
| Koelman, Philipus J. and Cornelia, House |
| Koenig Building |
| Koester, Nicholas, Building |
| Kolker House |
| Koren Library |
| Kreinbring Phillips 66 Gas Station |
| Kromer Flats |
| Kucheman Building |
| Kuhnen, Nicholas J., House |
| Kurtz, Glenn and Nell, Lustron Home and Garage |
| Kurtz House |
| Kyte, John and Mary Jane, Farmstead District |
| Ladora Savings Bank |
| Lake City Community Memorial Building |
| Lake City Public Library |
Data from United States Park Service and Wikidata
