Koonya is a locality on the Tasman Peninsula, Tasmania, Australia. It was established in 1841 as one of outlying parts of the network of penal colony sites centred on Port Arthur.
Under its former name of "Cascades", it was populated by at least 400 convicts.
After the Port Arthur penal colony was closed, and Van Diemen's Land was renamed "Tasmania", a number of places in Tasmania were renamed; "Cascades" was renamed "Koonya".
Koonya is part of the Tasman Council local government area.
A weather radar for the City of Hobart is in the Koonya locality.
Koonya hosts the annual Koonya Garlic Festival, a "one-day celebration".