 Stephen's great-grandfather, also George, (1706–1780), was the Attorney-General of West New Jersey in 1767-75 and commanded the Salem Light Horse during the Revolutionary War.Trenchard attended a school at Gambier, Ohio, founded by Bishop Philander Chase, with the intention of preparing for the ministry, but instead decided to follow the example of his father and uncle Joshua R. Sands, and join the Navy.After a probationary cruise in the Mediterranean aboard the frigate , he received his warrant as midshipman on October 23, 1834, and was ordered to the receiving ship "Concord", at Portsmouth.