His grandfather, Frederick Frelinghuysen (1753-1804), was an eminent lawyer, one of the framers of the first New Jersey constitution, a soldier in the War of Independence, and a member (1778-1779 and 1782-1783) of the Continental Congress from New Jersey, and in 1793-1796 of the United States senate; and his uncle, Theodore (1787-1862), was attorney-general of New Jersey from 1817 to 1829, was a United States senator from New Jersey in 1829-1835, was the Whig candidate for vice-president on the Clay ticket in 1844, and was chancellor of the university of New York in 1839-1850 and president of Rutgers College in 1850-1862.