The story
Oulainen was first mentioned in 1572 as Oulahais and as a part of the Pyhäjoki parish. A farm named Oulahainen was established earlier. The name comes from a dialectal word oulu meaning "flooding waters" (see also Oulu) and seems to suggest a Tavastian origin. Alpo Räisänen suggests that the name could be of Savonian or Karelian origin.
Oulainen became a chapel community in 1682, a parish in 1870, a kauppala in 1967 and a town in 1977.
From Wikipedia’s article on Oulainen, shared under CC BY-SA 4.0.4