Between 1782 and 1785, he was appointed Professor of Mathematics at the Royal Military Academy, Woolwich, where he remained until his death on 15 May 1821.
[1] He was a prolific writer, and wrote for the early volumes of Rees's Cyclopædia, about algebra, analysis and astronomy.
On Oct.7th, 1786 he married Brigette Newell with whom he had six children Charlotte, William, Mary, Sir Richard (Royal Engineer/Author), Humphrey and Charles.
His son Richard Henry Bonnycastle settled in Canada, where the family became quite well known in Winnipeg and Calgary.
His son, Charles Bonnycastle (1796-1840) became a Professor of Mathematics at the University of Virginia.