St. Mary's Episcopal Church is a historic Episcopal church on East Main Road in Portsmouth, Rhode Island, United States. Since 2023, St. Mary's Church has been listed on the National Register of Historic Places. The churchyard includes a cemetery with more than 2,000 interments.
Saint Mary's Church was opened to the public on June 17, 1849. The church was designed by architect Richard Upjohn in the Gothic Revival style and is made from local fieldstones with brownstone trim.
Saint Mary's Church was established through the philanthropy of Sarah Gibbs, who was the owner of nearby Oakland Farm. She was the sister of Ruth Gibbs Channing who was the wife of Unitarian minister and theologian William Ellery Channing.