Maryland - Criteria: C (architecture/engineering)
| Knocks Folly |
| Koons, Jacob, Farm |
| Koon, Thomas, House |
| Krieger, Seymour, House |
| Ladew Topiary Gardens and House |
| La Grange |
| LaGrange |
| Lake Drive Apartments |
| Lake-Evesham Historic District |
| Lake Roland Historic District |
| Langley Park |
| Lankford House |
| Lansdowne |
| Lantz-Zeigler House |
| Larkin's Hill Farm |
| Larkin's Hundred |
| Lauraville Historic District |
| Laurel High School |
| Laurel Railroad Station |
| Lauretum |
| La Vale Tollgate House |
| La Veille |
| Lawn, The |
| Lawyers Hill Historic District |
| Layton House |
| Leadenhall Street Baptist Church |
| Legg's Dependence |
| LeGore Bridge |
| Lehman's Mill Historic District |
| Leitersburg Historic District |
| Leonard House |
| Leverton, Jacob and Hannah, House |
| Lewis Mill Complex |
| Lexon |
| Liberty Hall |
| Linchester Mill |
| Linden |
| Linden |
| Linden Grove |
| Lindens, The |
| Lineboro Historic District |
| Linganore Farm |
| Linnwood |
| Linthicum Heights Historic District |
| Linthicum Walks |
| Linwood Historic District |
| Liriodendron |
| Little Elk Farm |
| Little Falls Meetinghouse |
| Little Montgomery Street Historic District |
| Llandaff House |
| Lloyd Street Synagogue |
| Loats Female Orphan Asylum of Frederick City |
| Locust Grove |
| Locust Point Historic District |
| Loft Historic District North |
| Loft Historic District South |
| Lombard Street Bridge |
| Lonaconing Furnace |
| Lonaconing Historic District |
| London Town Publik House |
| Long Green Valley Historic District |
| Long Hill |
| Long Island Farm |
| Long Meadows |
| Lord Baltimore Hotel |
| Lore, J. C., Oyster House |
| Lorraine Park Cemetery Gate Lodge |
| Loudon Park National Cemetery |
| Lovely Lane Methodist Church |
| Lowe, Joshua, House |
| Lower Deer Creek Valley Historic District |
| Loys Station Covered Bridge |
| Lutherville Historic District |
| Lyons, Joseph D., House |
| Lyric Theatre |
| MacAlpine |
| Maddox, George, Farm |
| Maddux House |
| Madison Avenue Methodist Episcopal Church |
| MAGIC (log canoe) |
| Magnolia Plantation |
| Maidstone |
| Makemie Memorial Presbyterian Church |
| Make Peace |
| Mannheim |
| Manokin Historic District |
| Manokin Presbyterian Church |
| Mansion House |
| Maple Leaf Farm Potato House |
| Maples, The |
| Marble Head |
| Marenka House |
| Marietta |
| Markell, George, Farmstead |
| Market Center |
| Marley Neck Rosenwald School |
| Marshall Hall |
| Marsh Mills |
| MARTHA LEWIS (skipjack) |
Data from United States Park Service and Wikidata
