Henry Ustick Onderdonk (March 16, 1789 – December 6, 1858) was the second Episcopal bishop of Pennsylvania.

[1] On returning to the United States, Onderdonk practiced medicine in New York before being ordained to the deaconate and priesthood by Bishop John Henry Hobart.

[1] In 1816, he went to western New York as a missionary and then returned east to become rector of St. Ann's Church in Brooklyn, remaining there for seven years.

However, bishop Kemp died of injuries received in a stage coach accident while returning from the consecration, so Onderdonk substituted in the Episcopal Diocese of Maryland until a successor was elected.

[3] In 1830, Onderdonk published Episcopacy Tested In Scripture, first published in the Protestant Episcopalian and then as tract by the Protestant Episcopal Tract Society, a defense of episcopacy based "on an appeal to the bible alone.