Alonnah is a small township on the western side of Bruny Island, Tasmania, facing the D’Entrecasteaux Channel. Originally named Mill’s Reef, it was renamed in the early 1900s after part of the Tasmanian aboriginal name for Bruny Island, Lunawanna-alonnah (a nearby township a little to its south being named Lunawanna. Mill’s Reef Post Office opened on 1 February 1905 and was renamed Alonnah in 1909. At the 2006 census, Alonnah had a population of 302.
Alonnah is the main location in Bruny Island for government facilities, including post office, police station, primary school, internet centre, community library, pharmacy, and health centre with nurses, a visiting doctor, physiotherapist, and other health practitioners. There is also a museum located in the court house, Bruny Hotel, and a small general store.
The Alonnah Dray track is an easy walking track of historical value, beginning at Alonnah jetty.