Thomas Balch Library is a history and genealogy library owned and operated by the Town Of Leesburg. Collections focus on Loudoun County, regional and Virginia history, genealogy, military history with special emphasis on the American Civil War, and ethnic history. Collection materials include books, periodicals, maps, visual collections, newspapers, oral histories,and manuscripts. Designated as an Underground Railroad research site. Lectures on history and genealogy are offered fall, winter and spring. Group tours and orientations are available on request. Books by Loudoun County authors may be purchased at the library.

One of the library's missions is collecting and preserving printed, manuscript, photographic, cartographic and genealogical documentation of Leesburg, Loudoun County and the surrounding region. The library actively seeks and welcomes donations of original business records, diaries, correspondence and photographs documenting life, culture and history of Leesburg and Loudoun County.

Library service in Leesburg started in 1907 when a small private subscription library society was opened in the Fishburn home at the corner of 102 Cornwall Street NW. In January of 1917 the library society moved to the Bentley House, 30 North King Street, with Virginia Aldridge serving as librarian; the annual subscription fee was $1. In 1918 a town library was established. Following fundraising efforts and construction, a building was dedicated 13 May 1922 as a memorial tribute to Thomas Balch (1821-1877), a native of Leesburg. The library operated for fifty years under a private Board of Trustees as a subscription library utilizing money from an endowment established by Thomas Willing Balch and Edwin Swift Balch, sons of Thomas Balch. It was staffed by part-time employees and volunteers. In1960 it became a free though segregated public library and in 1965 it was desegregated. In 1974 it joined with the Purcellville, Purcellville Bookmobile and Sterling Libraries as a branch of the recently established (1973) Loudoun County Public Library system serving the community as a full service public library. In July 1994 the County transferred ownership of the library to the Town of Leesburg to be operated as a history and genealogy library. The original building was designed by noted Washington DC architect Waddy B. Wood. In 2000 renovations and a sympathetic two-floor addition, designed by Bowie Gridley, doubled the library's size. Interior enhancements include murals depicting local history, portraits of distinguished local figures, and Thomas Moser furniture