The Third Congregational Society of Cambridge, Massachusetts, was incorporated June 16, 1827, and erected a brick meeting house on the corner of Thorndike and Third Streets in East Cambridge. The church was organized March 3, 1828, and was sometimes called the East Cambridge Church. It, along with the Lee Street Church, merged with the Cambridgeport Parish (whose meeting house was located on Austin Street) in 1885. As a result of the merger, the Cambridgeport Parish took on the corporate name and endowment of the Third Congregational Society. The Cambridgeport Parish/Third Congregational Society was also known as the Harvard Street Unitarian Church after it moved to a new building at 317 Harvard Street in 1911. It merged into the First Parish in 1939.
The library has the records of the Third Congregational Society (bMS 456), the Cambridgeport Parish (bMS 455), the Women's Alliance of the Harvard Street Church (bMS 14), and the Ladies Charitable Society of the Lee Street Church (bMS 15). [Photo of the church building on Harvard St.: bMS 15001/3]