Theodore William Dwight was born on July 18, 1822 at Catskill, New York, United States. He was the second son of Dr. Benjamin Woolsey Dwight and his wife, Sophia Woodbridge Strong, sister of Theodore Strong, the eminent mathematician. Benjamin Woodbridge Dwight was his elder brother. The family moved to Clinton, New York, in 1831. As a boy Theodore William was an omnivorous reader and possessed an exceptionally retentive memory.