Watertown's first Catholic society was formed in 1831. In 1838, they moved into a wooden church on Factory Street, previously the home of the First Baptist Church and named the church St. Mary's. The influx of Irish Catholic immigrants to Watertown during the 1840's and 1850's led the Irish members of St. Mary's to build a larger, brick structure on Massey Street in 1855. This new church was named St. Patrick's, after Ireland's patron saint. The current steeple of the church was added to the structure in 1885.
St. Patrick's opened its first school in 1885 on Massey Street. A larger school was later opened on the corner of Massey and Arsenal Street. In 1981, St. Patrick's school was moved to South Massey Street. In 2004, the school was renamed Immaculate Heart Intermediate School.