Complex sentence: The first resident priest in Vermont was Rev. Jeremiah O'Callaghan, who in 1830 was sent by Bishop Fenwick to Vermont, and visited successively Wallingford, Pittsford, Vergennes, and Burlington.
Split into simpler sentences: The first resident priest in Vermont was Rev. Jeremiah O'Callaghan in 1830. He was sent by Bishop Fenwick to Vermont, and visited successively Wallingford, Pittsford, Vergennes, and Burlington.