Benjamin Treadwell Onderdonk (July 15, 1791, New York - April 30, 1861, New York) was the Bishop of the Episcopal Diocese of New York from 1830–1861. A member of a prominent Hempstead family, Onderdonk graduated from Columbia College, now Columbia University, where he was president of the Philolexian Society. He studied theology under Bishop John Henry Hobart and was a member of the Episcopal Theological Society between 1810 and 1811. He married Eliza Handy. He presided over the Diocese during a period of expansion and was instrumental in the creation of numerous parishes, but is best remembered as one of the most controversial figures in the history of the Episcopal Church of the United States.