John Deyell (c. 1775 – November 21, 1878) was assistant to the original surveyor of Cavan Township in Durham County, Ontario, and founder of the town of Millbrook, Ontario.
He was born in Drum, County Monaghan, Ireland, about 1775, and died on November 21, 1878 in Centreville, Cavan Township. A farmer who settled on 3rd Concession, Cavan, he established the first gristmill and sawmill on the stream at what is now called Millbrook. He also built the nucleus of a village called Centreville, since his farm was located on the midpoint of the Port Hope to Peterborough highway. In 1833 he endowed land for its first church, the Centreville Presbyterian Church, still flourishing today. Anticipating commercial traffic, he built a hotel/tavern on his farm, and his well-remembered sign, which hung out for several decades, bore the motto – "Live and Let Live." The area's first schoolhouse was also built on Deyell's farm - to which he gave a grant of an acre of land. While Millbrook survived and prospered, Centreville never grew beyond a cluster of houses around the church, now graced however with a beautiful stained glass window installed in 1931 in memory of John Deyell and his wife Margaret and Cavan's other early pioneers. Deyell's headstone is still visible in the church's small cemetery.