Frederick Theodore Frelinghuysen (August 4, 1817 - May 20, 1885) was a member of the United States Senate from New Jersey and a member of the Electoral Commission that decided the 1876 Presidential election. As a Republican, he voted with the eight-member majority on all counts.

He also served as Secretary of State from 1881-1885, appointed by President Chester A. Arthur.

He was born in Millstone, New Jersey. He was a delegate to Republican National Convention from New Jersey, 1860, the New Jersey state attorney general, 1861-66, and a U.S. Senator from New Jersey, 1866-69, 1871-77. He died in Newark, New Jersey and was buried at Mt. Pleasant Cemetery in Newark.