From the record
“The Jefferson Barracks Military Post is located on the Mississippi River at Lemay, Missouri, south of St. It is the oldest operating U.S. military installation west of the Mississippi River, and it is now used as a base for the Army and Air National Guard.”
Wikipedia article Jefferson Barracks Military Post, CC BY-SA 4.0.
One of 663 National Register listings published here for St. Louis County · listed in 1972 · category: District · built in 1826.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service

