(previously Frederiksstad) (literally Fredrik's Town) is a city and municipality in Østfold county Norway. The administrative centre of the municipality is the city of Fredrikstad. The city of Fredrikstad was founded in 1567 by King Frederik II and established as a municipality on 1 January 1838. The rural municipality of Glemmen was merged with Fredrikstad on 1 January 1964. The rural municipalities of Borge Onsøy Kråkerøy and Rolvsøy were merged with Fredrikstad on 1 January 1994.