As far as we know, the only other community in the world with the same name is in the state of Victoria, Australia.
Whilst some ten times larger than its Cumbrian cousin, the other Casterton is described as "a relatively small rural centre of about 2000 people located on the banks of the Glenelg River in a valley surrounded by rolling hills some 350 km west of Melbourne Victoria. It is a service centre to a large pastoral, mixed farming, timber-producing and dairying district near the South Australian border. Casterton has a golf course, a racecourse, a caravan park, a sports and leisure centre".
There are no formal links between the two, but Cumbrian legend has it that the Australian settlement was founded by two brothers named Kirkby. The Australian website says merely that "the townsite of Casterton emerged on a crossing place along the Glenelg River. Surveyed in 1840 it was named after a settlement in the north of England"