Illinois - Area of significance: Architecture
| Lathrop, Bryan, House |
| Lathrop, Julia C., Homes |
| Laurent, Kenneth and Phyllis, House |
| Lawrence County Courthouse |
| Lawson, Victor F., House YMCA |
| Lazy A Motel |
| Leaning Tower of Niles, The |
| Lebanon Historic District |
| Legler, Henry E., Regional Branch of the Chicago Public Library |
| Leiter II Building |
| Lemont Central Grade School |
| Lemont Downtown Historic District |
| Lemont Methodist Episcopal Church |
| Leonard, Clifford Milton, Farm |
| LeRoy Commercial Historic District |
| Lesem, S.J., Building |
| Lewis, John W., House |
| Lewis, Lloyd, House |
| Lewis Round Barn |
| Libertyville Downtown Historic District |
| Library Hall |
| Library-University of Illinois at Urbana-Champaign |
| Lichtstern House |
| Lincoln Building |
| Lincoln Courthouse Square Historic District |
| Lincoln Park |
| Lincoln Park, South Pond Refectory |
| Lincoln Public Library |
| Lindemann and Hoverson Company Showroom and Warehouse |
| Linden Avenue Terminal |
| Linden Park Place-Belle Avenue Historic District |
| Lind, Jenny, Chapel |
| Linn, Howard and Lucy, House |
| Litchfield Elks Lodge No. 654 |
| Little Brick House |
| Livingston County Courthouse |
| Lockport Historic District |
| Loeb, Ernest, House |
| Logan Square Boulevards Historic District |
| Loop Retail Historic District |
| Loucks, Charles N., House |
| Louisville and Nashville Depot |
| Lou Mitchell's Restaurant |
| Ludington Building |
| Lumber Exchange Building and Tower Addition |
| Lumpkin Heights and Elm Ridge Subdivision Historic District |
| Lundberg, Charles, House |
| Lunsford-Pulcher Archeological Site |
| Lynch, Timothy J., House |
| Lyons Township Hall |
| Macktown Historic District |
| Macomb Courthouse Square historic District |
| Madison Theatre |
| Madlener, Albert F., House |
| Maeystown Historic District |
| Magnolia Manor |
| Maher, George W., House |
| Main Street Historic District |
| Majestic Theatre |
| Malden Towers |
| Mandel Brothers Warehouse Building |
| Mandel, Mr. Fred L., Jr., House |
| Manhattan Building |
| Manor House |
| Maple Avenue Maple Lane Historic District |
| Maple Court Apartments |
| Marine Chapter House |
| Marion Veterans Administration Hospital Historic District |
| Mark, Caroline, House |
| Mark Twain Hotel |
| Marquette Apartments |
| Marquette Building |
| Marshall Business Historic District |
| Marshall Field and Company Store |
| Marshall Hotel |
| Marsh, William W., House |
| Martin House |
| Martin, Pierre, House |
| Martin, Sarah, House |
| Mary A. Todd School |
| Marywood Academy |
| Masonic Temple |
| Masonic Temple Building |
| Masonic Temple Building |
| Mason, Paris, Building |
| Mattfeldt, Theodore H. O., House |
| Mattis, George and Elsie, House |
| Maverick Lloyd, Lola, House |
| Maxwell-Briscoe Automobile Company Showroom |
| Mayfair Apartments |
| Maynard, Isaac N., Rowhouses |
| Maywood Fire Department Building |
| McAuley School District No. 27 |
| McClintock, John and Amelia, House |
| McClure, Thomas J. and Caroline, House |
| McClurg Building |
| McCormick, Charles Emmor, House |
| McDonough County Courthouse |
| McFarland House |
| McGrath, John, House |
Data from United States Park Service and Wikidata
