Like so many other communities, Os community has also derived its name from the farm where the parish church was situated. Thus it is that the farm Os, the farm by the river mouth, has given its name to the parish and later on to the municipality.
The oldest church on the farm Os was probably built at the latest in 1050 and already the first priests probably lived on the farm.
The oldest building still remaining on the farm is a smoke house about 6,25 x 5.96 meters, built around 1380. This building was used as a rectory for around 300 years.
Around 1650 a new rectory was built. This was a so-called glass house (a house with windows) in two stories, which was joined to the gable of the old house with a hallway between the two houses. This was the building style of the Middle Ages.
When the priest Jersin arrived in the community in 1816 to settle in the rectory, the buildings were very dilapidated. In 1820 a new rectory was built and the old houses repaired.
The main building from 1820 was pulled down when the new rectory was built in 1920 based on Ole Landmarks’s drawings in cultivated classicism. This house still is a rectory in Os. On the same farm the two houses from the 1300s and 1600s are still standing.