In addition to his pastoral duties, Mason was elected the first provost of Columbia College in 1801 and served as a trustee for 26 years. In 1804 he founded what would later become the Union Theological Seminary, the oldest independent Christian seminary in the US. Also in 1804 he helped found the New-York Historical Society. In his later years he served as President of Dickinson College.
Mason died in December 1829 and was buried in the Eighth Street Church cemetery. Twenty years later he was reinterred in the New York Marble Cemetery in Vault 139, belonging to his sons Abraham and John Lefferts Mason.
Written by: Tiffany McKerahan (a 5th-great-granddaughter,) 2017