Horatio Seymour Jr. (January 8, 1844 – February 21, 1907) was an American civil engineer, surveyor and politician from New York.

On December 1, 1874, he was appointed Assistant Engineer on the New York State Canals.

He was New York State Engineer and Surveyor from 1878 to 1881, elected on the Democratic ticket in 1877 and 1879.

Later he returned to Utica and continued to work as a general practicing engineer.

He founded the Huron Mountain Club along with John Munro Longyear.