- Labor History Collection of Publications and Artifacts, 1937/19591
- Lloyd Layman Papers regarding Firefighting, 1918/196814
- Lonnie Miller, Compiler, Research Papers Regarding Coal History in Southwestern Pennsylvania, 1887/2014, bulk 1940/19904
- Lorilla Frances Bullard Tower, Doctor, Papers, 1894/19043
- Louis and Sallie Bennett, Papers of a Lewis County Family, 1870/19304
- Louise McNeill, Poet, Papers, 1861/1993, bulk 1970/19935
- Lyric Theatre Collection, 1922/2006, bulk 1922/19794