It is one of four congregations that have constituted the parish of St. Thomas in the Episcopal Diocese of Washington, the others including the Church of the Atonement in Cheltenham, the Chapel of the Incarnation in Brandywine, and St. Simon's Mission also in Croom.

In 1850, St. Thomas' became its own parish and undertook Gothic Revival renovations and expansion under the direction of New York City architect, John W. Priest, an associate of Andrew Jackson Downing.

[2] One of the original founders and benefactors of St Thomas's church was Benedict Swingate Calvert (1730-1788) who was a Maryland Loyalist during the American Revolution.

His mother's identity is not known and, as he was illegitimate, he was not able to inherit his father's title or estates, which passed instead to his half brother Frederick Calvert, 6th Baron Baltimore (1731–1771).

Calvert became wealthy through proprietarial patronage and became an important colonial official, but he would lose his offices and his political power, though not his land and wealth, during the American Revolution.