Eastleigh is a town in Hampshire, England, between Southampton and Winchester. It is the largest town and the administrative seat of the Borough of Eastleigh, with a population of 24,011 at the 2011 census. The town lies on the River Itchen, one of England's premier chalk streams for fly fishing, and a designated site of Special Scientific Interest. The area was originally villages until the 19th century, when Eastleigh was developed as a railway town by the London and South Western Railway.