Thornbury is a market town and civil parish in the South Gloucestershire unitary authority area of England, about 12 mi north of Bristol. It had a population of 12,063 at the 2011 census. The population has risen to 14,496 in the 2021 census. Thornbury is a Britain in Bloom award-winning town, with its own competition: Thornbury in Bloom. The earliest documentary evidence of a village at "Thornbyrig" dates from the end of the 9th century.