The story
The municipality is named after the village of Petäjävesi (Petäjäveden kirkonkylä), which in turn is named after lake Petäjävesi, lit. 'pine water' (i.e. 'pine lake', compare Leppävesi and Pihlajavesi). Originally part of Jämsä, the area became a subordinate parish under it in 1728 as Kuivasmäki. It became an independent parish under the name Petäjävesi in 1867.
From Wikipedia’s article on Petäjävesi, shared under CC BY-SA 4.0.4
