Arlesey is a small formerly industrial town and civil parish in the unitary authority of Central Bedfordshire. It stands near the border with Hertfordshire, about three miles north-west of Letchworth Garden City, four miles north of Hitchin and six miles south of Biggleswade. Arlesey railway station provides services to London, Stevenage Peterborough and northward beyond. The station opened in 1988 under the Network South East branch of the nationalised British Rail company. An earlier station had been called "Arlesey & Henlow" and "Three Counties", a reference to the nearby hospital for people with psychological difficulties (at the time called "mentally ill"). The hospital admitted patient from Bedfordshire, Buckinghamshire and Hertfordshire: hence "Three Counties". The original station was closed to passengers in the 1960s.
Arlesey Town Football Club has their ground to the south of the town.
Spelling variations may include 'Arlychesey', seen in 1430, the home of the complainant William Bocher, husbandman. and 'Arlythesey', seen in 1418. That these refer to Arlesey is suggested in an earlier document: the index to one of the Patent Rolls of King Richard II.
Residents have claimed it to be the longest town in Britain.
Arlesey Old Moat and Glebe Meadows nature reserves are just north of the town.
Major employers in Arlesey used to be the Fairfield Hospital (now re-developed as the residential Fairfield Park) and the former brickworks (producers of the Arlesey Whites bricks seen in many local buildings). Some of the clay pits used by the brickworks are now lakes and there are also two disused Portland Cement Company chalk pits, one of which is the Blue Lagoon, which hosts fishing and sailing clubs. Although the lake is private, large numbers of people go there to swim. There have been a number of drownings that have been reported in the national news. In 2001 three children died when the car they were in was accidentally driven into the lake. Most recently a teenager drowned while swimming in April 2007.