Selby is a market town and civil parish in North Yorkshire, England, south of York on the River Ouse. In the 2021 UK Census it had a population recorded at 19,760. The town was historically part of the West Riding of Yorkshire until 1974. From 1974 to 2023 the town was the administrative centre of the Selby District. Selby once had a large shipbuilding industry and was an important port on the Selby Canal, which brought trade from Leeds. The town's origins date from the establishment of a Viking settlement on the banks of the River Ouse. Archaeological investigations in Selby have revealed extensive remains, including waterlogged deposits in the core of the town dating from the Roman period onwards. It is believed that Selby originated as a settlement called Seletun, which was referred to in the Anglo-Saxon Chronicle of AD 779. The place name 'Selby' is first attested in a Yorkshire charter 1030, where it appears as Seleby. It appears as Selbi 1050. The name is thought to be a Scandinavian form of Seletun, meaning 'sallow tree settlement'. The town of Selby is on the main route north from the Midlands and is the traditional birthplace of King Henry I, fourth son of William the Conqueror, in 1068/69; the connection is supported by William and his wife Matilda's unique joint charter of Selby Abbey, far to the north of their usual circuit of activities, which was founded for Benedict of Auxerre in 1069 and subsequently supported by the de Lacy family. King Henry I is reputed to have been born there in 1068. A notable feature of the abbey is the 14th-century Washington Window, featuring the heraldic arms of the ancestors of George Washington, the first president of the United States. The design is often cited as an influence for the Stars and Stripes flag. It is said that the abbey was founded when Benedict saw three swans on a lake in Selby, which he took as a sign of the Father, Son and Holy Ghost, and that is why the official crest of Selby Abbey is three swans.