Illinois - Criteria: C (architecture/engineering)
| Hunt House |
| Hyde Park-Kenwood Historic District |
| IBM Building |
| Iles, Elijah, House |
| Illinois and Michigan Canal |
| Illinois Central Railroad Water Tower and Pump House |
| Illinois Industrial School for Girls |
| Illinois Institute of Technology Academic Campus |
| Illinois Iron Furnace |
| Illinois National Guard Armory |
| Illinois Route 4-North of Auburn |
| Illinois State Bank Building |
| Illinois State Capitol |
| Illinois Traction Building |
| Illinois Traction System Mackinaw Depot |
| Immaculata High School |
| Immanuel Evangelical Church |
| Independence Park |
| Indian Boundary Park |
| Indian Ford Bridge |
| Indian Hill Manor and Farm Historic District |
| Indian Statue |
| Inland Steel Building |
| Inman Hotel |
| International Tailoring Company Building |
| Ives, Gideon, House |
| Jackson County Courthouse |
| Jackson Park Historic Landscape District and Midway Plaisance |
| Jackson Shore Apartments |
| Jacksonville Downtown Historic District |
| Jacksonville Historic District |
| Jacoby, Lysander, House |
| James, Jean Butz, Museum of the Highland Park Historical Society |
| Jameson, H.D., House |
| Jarrot, Nicholas, Mansion |
| Jarvis, William W., House |
| Jefferson Park |
| Jeffery-Cyril Historic District |
| Jehle, Louis, House |
| Jensen, Chris, Round Barn |
| Jensen, Jens, Summer House and Studio |
| Jersey County Courthouse |
| Jerseyville Downtown Historic District |
| Jewelers' Building |
| Jewish People's Institute |
| Johnson County Courthouse |
| Johnson, Olof, House |
| Joilet YMCA |
| Joliet East Side Historic District |
| Jones House |
| Jubilee College |
| Judah, Noble, Estate |
| Judd, C. H., House |
| Judson, The |
| Kankakee County Courthouse |
| Kappa Delta Rho Fraternity House |
| Kappa Kappa Gamma Sorority House |
| Kappa Sigma Fraternity House |
| Kenilworth Club |
| Kent, Sydney, House |
| Kenwood Evangelical Church |
| Kewanee Public Library |
| Keys, Alvin S., House |
| Keystone Building |
| Kickapoo Building |
| Kimball, William W., House |
| King, Patrick J., House |
| Klunk, Michael, Farmstead |
| Knuessl Building |
| Koerner, Gustave, House |
| Krause Music Store |
| K-Town Historic District |
| Kuppenheimer, Louis B., Jr., House |
| La Grange Lock and Dam Historic District |
| La Grange Village Historic District |
| Lake Bluff Uptown Commercial Historic District |
| Lake Forest Cemetery |
| Lake Forest Historic District |
| Lake-Peterson House |
| Lake Shore Apartments |
| Lakeside Press Building |
| Lake-Side Terrace Apartments |
| Lakeview Historic District |
| Lamoine Hotel |
| Lamont, Robert P., House |
| Lampert-Wildflower House |
| Lanzl, Haerman, House |
| Larson, Mads C., House |
| LaSalle Downtown Commercial District |
| LaSalle Street Auto Row Historic District |
| Lathrop, Bryan, House |
| Lathrop, Julia C., Homes |
| Laurent, Kenneth and Phyllis, House |
| Lawrence County Courthouse |
| Lawson, Victor F., House YMCA |
| Lazy A Motel |
| Lebanon Historic District |
| Legler, Henry E., Regional Branch of the Chicago Public Library |
| Leiter II Building |
| Lemont Central Grade School |
Data from United States Park Service and Wikidata
