The story
Hartola may have been mentioned as early as 1398 (ut ecclesia parrochialis Hartola Aboensis dioceses), however this may have also referred to Hattula. It was originally a part of the parish of Sysmä. At least between 1540 and 1729, it was called Koskipää, after which the name Hartola appears again.
Hartola became an independent parish in 1784. It was also granted the Swedish name Gustav Adolfs. In Finnish, the parish was also known as Kustavus, Kustavuksenpitäjä and Kustaanpitäjä, but the name Hartola was still in use. By the late 1800s, Hartola had become the sole name for the parish.
Joutsa was a part of Hartola until 1860, while Leivonmäki was a part of Hartola until 1880.
From Wikipedia’s article on Hartola, Finland, shared under CC BY-SA 4.0.5