Portchester is a locality and suburb 10km northwest of Portsmouth, England. It is part of the borough of Fareham in Hampshire. Once a small village, Portchester is now a busy part of the expanding conurbation between Portsmouth and Southampton, on the A27 main thoroughfare. Its population according to the 2001 Census was approximately 17,000 residents.
As well as the castle, its parish church St Mary's and the abundance of historic houses in Castle Street, this suburb is well placed for waterfront leisure activities, being only a short distance from the UK's third largest marina at 'Port Solent', and from the historic city of Portsmouth and the market town of Fareham.