From the Wikipedia page 
The National Personnel Records Center is an agency of the National Archives and Records Administration, created in 1956. It is divided into two large Federal Records Centers located in St. Louis, Missouri.
The records centers which comprise the National Personnel Records Center are the Military Personnel Records Center, located on Archives Drive in Spanish Lake, Missouri, and the Civilian Personnel Records Center located between two facilities: one on Winnebago Street in downtown St. Louis, Missouri and the other on Boulder Boulevard in Valmeyer, Illinois.
A separate building, which houses archived Navy and Marine Corps military records (now released to the public as of 2005) is in Overland, Missouri.
A major fire on July 12, 1973 destroyed approximately one-third of its 52 million official military personnel files.
The website is