Selfoss (Icelandic pronunciation: ​[ˈsɛlˌfɔsː]) is a town in southern Iceland on the banks of the Ölfusá river. It is the seat of the municipality of Árborg. The Icelandic Route 1 runs through the town on its way between Hveragerði and Hella. The town is a centre of commerce and small industries with a population of 9000 (2021), making it the largest residential area in South Iceland.