Theodore Frelinghuysen was born in 1787 in
Franklin Township, Somerset County, New Jersey, to
Frederick Frelinghuysen and Gertrude Schenck. Frelinghuysen's siblings included: Catharine Frelinghuysen;
John Frelinghuysen (1776–1833) the General who married Louisa Mercer and after her death married Elizabeth Mercereau Van Vechten; Maria Frelinghuysen (1778–?); and Frederick Frelinghuysen (1788–1820) the lawyer who married Jane Dumont. His great-grandfather
Theodorus Jacobus Frelinghuysen was a minister and theologian of the
Dutch Reformed Church, influential in the founding of
Queen's College, now
Rutgers University, and one of four key leaders of the
First Great Awakening in Colonial America. Theodore was the uncle of
Frederick T. Frelinghuysen and great-great-grandfather of
Henry Cabot Lodge Jr. Rodney Frelinghuysen, who represented
New Jersey's 11th congressional district, is a descendant. Frelinghuysen married Charlotte Mercer in 1809, but she died in the same year. They had no children together, but when Theodore's brother, Frederick Frelinghuysen (1788–1820) died, Theodore adopted his son,
Frederick Theodore Frelinghuysen (1817–1885), who would later become
Secretary of State. Theodore Frelinghuysen remarried in 1857 to Harriet Pumpelly. He graduated from the College of New Jersey (now
Princeton University) in 1804 and studied law under his brother John Frelinghuysen, and later,
Richard Stockton. He was admitted to the bar as an attorney in 1808 and as a counselor in 1811, and set up a law practice in
Newark during this time period. In the
War of 1812, he was a captain of a company of volunteers. by
John William Draper possibly depicts Frelinghuysen in 1839, making it one of the earliest known photographs of an American. ==Political career==