The Post House is a historic house located at 1516 State St. in Alton, Illinois, United States. William Post, a steamboat captain who later became mayor of Alton, built the house in 1837-38. The brick and limestone house is designed in the Greek Revival style. The house's front facade features four Doric columns topped by an entablature and a pedimented gable end. The front porch of the house wraps around both sides, each of which has an additional column and a pilaster. The cornice and front pediment are both dentillated. James Patterson, owner of the Illinois Iron Works, purchased the house in 1854; Patterson may have added the iron porch railing.