Casterton is a small village and civil parish close to Kirkby Lonsdale on the River Lune in the south east corner of Cumbria, England. In the 2001 census the parish had a population of 500, decreasing at the 2011 census to 425. The village is situated approximately 5 miles (8.0 km) from junction 36 (Kendal and the Lakes exit) of the M6 motorway, near the intersection of the A65 Kendal to Leeds road, and the A683 which runs up the Lune valley from the port of Heysham to the market town of Kirkby Stephen.