Østfold County Municipality (Norwegian: Østfold fylkeskommune) is the regional governing administration of Østfold county in Norway. The county municipality was established in its most early form on 1 January 1976 when the law was changed to allow elected county councils in Norway. The county municipality was dissolved on 1 January 2020, when Østfold was merged with the neighboring counties of Akershus and Buskerud, creating the new Viken county which is led by the Viken County Municipality. On 1 January 2024, following the dissolution of Viken county, the county municipality of Østfold was re-established. The administrative seat is located in Sarpsborg.
The Østfold county council (Norwegian: Fylkestinget) is made up of 35 representatives that are elected every four years. The council essentially acts as a parliament or legislative body for the county and it meets several times each year. The council is divided into standing committees and an executive board (fylkesutvalg) which meets considerably more often. Both the council and executive board are led by the County Mayor (fylkesordfører) who held the executive powers of the county.