Siuntio (ˈsiu̯ntio; Sjundeå) is a municipality of Finland located in the Uusimaa region in the province of Southern Finland. Its neighboring municipalities are Ingå to the west, Kirkkonummi, to the east, Lohja to the north-west, and Vihti to the north. It is west of Helsinki. As of 2021, the population was with a population density of . The municipality covers an area of , of which is water. The municipality is bilingual. The majority of the population are Finnish-speakers with a minority of Swedish-speakers, though a majority spoke Swedish until the 1980s. Siuntio's motto is "Ota rauhallisesti - Ta det lugnt", meaning "take it easy", written in both Finnish and Swedish respectively. The new motto came into use following the municipality's rebranding program together with the new logo in March 2021. During Swedish rule over Finland. the official name was "Sjundeå", which basically means "seventh river." It is strongly believed that the name refers to Siuntio's river being seventh towards the east of Finland's former capital Turku. Siuntio has been inhabited since the Stone Age, with the oldest evidence of farming settlements discovered in the river valley around the medieval Siuntio church. A Bronze-Age burial site can also be found near the church, on top of the Krejansberget hill. The oldest known document mentioning Siuntio is from the year 1382, addressing a donation for the Church of St. Lawrence in Lohja. During the Middle Ages Siuntio became an area of importance after two large manor houses, Suitia and Sjundby, were built there. The earliest mention of Suitia Manor House is from 1420 in a document addressing a border conflict between Suitia estate and an estate owned by the bailiff of Häme Castle. Later, the estate came to the possession of the influential Fleming family. Over time, the Flemings acquired new land for the Suitia estate; at one point, Suitia had its own harbor by the sea near the mouth of Pickala river. The Flemings also built the first ironworks in Finland, located on the Suitia Manor House's land, in the 1530s.