I have given some thought to the origin of the Cowley family name. This is probably associated with a place named Cowley (1). There is a Cowley in Gloucestershire today a few miles south of Cheltenham, which could be the ancient origin of the name, though FamilySearch (FS) has no Cowley christenings between 1595 and 1812. However, Cowley baptisms at Slimbridge go back to at least 1748, and if the family lived at there since the mid-1600s a more likely candidate would Coaley, about 3 or 4 miles east of Slimbridge. Although its modern name is Coaley, it was known as Cowley in “ye time of Samuel Winney, who had possession of ye Vicaridge of Cowley, January 1st, 1654/5” (2), though there are no Cowley baptisms listed there either. Nonetheless, there were also many baptisms in places near to Slimbridge, including Fretherne, Eastington and Frampton, all going back to the 1600s, so Coaley looks the more likely origin. There are other places named Cowley, of course, but even in Cowley, Oxfordshire, FS 1689-1854 records no Cowley baptisms and only one Cawley marriage in 1835.
1. Reaney and Wilson, 2005, Oxford Dictionary of English Surnames, Oxford University Press, p114.
2. Gloucestershire Genealogy: Coaley Parish Registers