Brentsville became the center of Prince William County after the Commonwealth of Virginia created the town in 1820 at the county's geographic center on land seized from Robert Bristow, a loyalist during the American Revolution, and the brick courthouse and jail were built there in 1822, around which a thriving community grew. Residents had sought to move the county seat from Dumfries to a more central location as population increased in the early 1800s. Before the Civil War, the town tried to secure the Orange and Alexandria Railroad, but the steep banks of Broad Run led the tracks to be laid three miles west at Bristoe Station instead. During the Civil War, Confederate and Federal soldiers encamped in town demolished more than 19 buildings, and Brentsville never recovered from the combined effects of wartime destruction and the railroad bypass, culminating in the county seat's removal to Manassas in 1893. After the war, Union Church was established in 1874 to serve local residents of different denominations, and from 1929 to 1944 a one-room schoolhouse on the site was used by children in the Brentsville area. The site also includes an 1850s house once owned by the Haislip-Hall family, moved to Brentsville in 2000 from Greenwich, Virginia, to depict the home and farm life of a 19th-century farm family. Broad Run also shaped local settlement and industry, as early European settlers built along its banks for water and transportation, mills lined it in the 18th and 19th centuries, and its watershed extends about 140 square miles before joining Cedar Run to form Occoquan Creek.