Basildon ( BAZ-il-dən) is the largest town in the borough of Basildon, within the county of Essex, England. It had a recorded population of 107,123. In 1931, the town had a population of 1,159.

It lies 26 miles (42 km) east of Central London, 11 miles (18 km) south of the city of Chelmsford and 10 miles (16 km) west of the city of Southend-on-Sea. Nearby towns include Billericay to the north-west, Wickford to the north-east and South Benfleet to the south-east. It was created as a new town after World War II in 1948, to accommodate the London population overspill from the conglomeration of four small villages, namely Pitsea, Laindon, Basildon (the most central of the four) and Vange.

The local government district of Basildon, which was formed in 1974 and received borough status in 2010, encapsulates a larger area than the town itself; the two neighbouring towns of Billericay and Wickford, as well as rural villages and smaller settlements set among the surrounding countryside, fall within its borders. Basildon Town is one of the most densely populated areas in the county. The parish of Basildon was abolished to create Billericay on 1 January 1937.

Some of Basildon's residents work in Central London, due to the town being well connected in the county to the City of London and the Docklands financial and corporate headquarters districts, with a 36–58 minute journey from the three Basildon stations on the C2c to London Fenchurch Street. Basildon also has access to the City via road, on the A127 and A13.