Castle Sowerby is a civil parish in the Eden District of Cumbria, England. In 2001 it had a population of 337, increasing to 344 at the 2011 Census, and includes the hamlets of How Hill, Millhouse, Newlands, Sour Nook, Southernby and Sowerby Row. Located 3 miles (4.8 km) north of Sowerby Row is Thistlewood Farmhouse, consisting of a pele tower probably built in the early 15th century, with 16th century alterations, and an extension built in the late 17th century. The 12th century and later St Kentigern's Church is Grade II* listed.