Forthside is a rural locality in the local government area (LGA) of Devonport in the North-west and west LGA region of Tasmania. The locality is about south-west of the town of Devonport. The 2016 census recorded a population of 81 for the state suburb of Forthside.
Forthside is a confirmed locality.
The Forth River forms much of the western boundary, and the Don River forms a small part of the eastern.
Route C145 (Forthside Road / Bellamy Road) runs through from north-west to east.