From the record
“Fort Lancaster is a former United States Army installation located near Sheffield, Texas. The fort was established in 1855 on the San Antonio-El Paso Road to protect migrants moving toward California through Texas.”
Wikipedia article Fort Lancaster, CC BY-SA 4.0.
One of 3 National Register listings published here for Crockett County · listed in 1971 · category: Site.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service