Thornbury is a market town and civil parish in the South Gloucestershire unitary authority area of the ceremonial county of Gloucestershire, England, about 12 miles north of Bristol. It had a population of 12,063 at the 2011 Census, estimated at 12,459 in 2019. 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. Domesday Book noted a manor of "Turneberie" belonging to William the Conqueror's consort, Matilda of Flanders, with 104 residents.