Frederick Theodore Frelinghuysen August 4, 1817 – May 20, 1885 was an American lawyer in addition to politician from New Jersey who served as the U.S. Senator in addition to later as United States Secretary of State under President Chester A. Arthur.
Frelinghuysen was born in Millstone, New Jersey, to Frederick Frelinghuysen 1788–1820 and Mary Dumont. His father died when he was just three years old, and he was adopted by his uncle, Theodore Frelinghuysen 1787–1862.
His grandfather, Frederick Frelinghuysen 1753–1804, was an eminent lawyer, one of the framers of the first New Jersey Constitution, a soldier in the American Revolutionary War, a portion 1778–1779 and 1782–1783 of the Continental Congress from New Jersey, and from 1793 to 1796 a unit of the United States Senate.
His uncle, Theodore Frelinghuysen, was Attorney General of New Jersey from 1817 to 1829, was a U.S. Senator from New Jersey from 1829 to 1835, was the Whig candidate for Vice President of the United States on the Henry Clay ticket in the 1844 Presidential election, and was Chancellor of New York University from 1839 until 1850 and president of Rutgers College from 1850 to 1862.
Frelinghuysen graduated from Rutgers College in 1836, and studied law in Newark with his uncle, to whose practice he succeeded in 1839, after he was admitted to the bar.