St. Louis County Library (SLCL) serves residents of St. Louis County, Missouri, United States. It is the busiest public library in Missouri, circulating more than 12 million items in 2011. It consists of 20 branches, including the Headquarters branch, which is located at 1640 S. Lindbergh Blvd in Ladue. SLCL is unrelated to the St. Louis Public Library, which serves the city of St. Louis. SLCL services the St. Louis county. The library was founded in 1947. It is supported by the St. Louis County Library District, which includes most of St. Louis County.