[3][4] It is located in the province of Southern Finland and is part of the Päijänne Tavastia region.

Lake Pääjärvi is situated at the border between Hämeenkoski and Hämeenlinna (formerly Lammi).

It was initially a part of the Lammi administrative division and the Hauho parish.

Koski was first mentioned as a separate parish in 1410, but it was merged into Lammi as a chapel community in 1540.

The name Hämeen-Koski was first suggested for the parish in 1897 by Väino Wallin to distinguish it from Koski Tl, at the time still a part of Marttila.