In 1800 Seymour married Lucy Case of
Addison. They were the parents of four sons and two daughters. Lucy Case Seymour died in 1838. Seymour's son Ozias (1801–1861) was an attorney in Middlebury, and served as Addison County State's Attorney. His son
Horatio Seymour Jr. (1813–1872) was an attorney in
Buffalo, New York and served as
Erie County's surrogate court judge. Seymour's son Moses was a merchant and farmer, first in Middlebury, and later in
Geneva, Wisconsin, and served in local office including president of Geneva's board of village trustees. His daughter Mary was 16 when she died of tuberculosis in 1821. Seymour's daughter Emma was the wife of Phillip Battell and they were the parents of two children before her death in 1841. Their daughter, also named Emma (1837–1900), was the wife of
John Wolcott Stewart. His son Henry served in the
United States Army during the
Second Seminole War, and died in
Boston in 1847. ==Legacy==