Leigh-on-Sea Leigh-on-Sea is a civil parish administered as part of Southend-on-Sea, in Essex, England. In 1996, it became a civil parish, and a town council was created, funded by an increased council tax rate in the area. The parish, which is the only one in Southend, had a population of 20,737 according to the 2001 census. A survey by Halifax Estate Agents, published in the Evening Standard newspaper in 2007, placed Leigh-On-Sea as being the second best place to live in England after Christchurch, Dorset.