It would seem that Dr Hill was based in America.
http://upfront.ngsgenealogy.org/2012/09/new-voices-of-geneal...

However, out of interest, there were several Colwill's in Ilfracombe, North Devon and some ran a coaching company in the area

http://www.focusonilfracombe.co.uk/wp-content/uploads/2012/0...
http://www.lerwill-life.org.uk/history/coaching.htm

Would suggest contacting Ilfracombe Museum, Devon, England. They have some info on local people.
http://www.ilfracombemuseum.co.uk/

Good luck.Sue