 Jennings served as a director of Standard Oil of Ohio and then as a trustee of the Standard Oil Trust that resulted from the company's reorganization in 1882.On December 13, 1854, he married Esther Judson Goodsell (1828–1908) in Fairfield.Her sister Almira Geraldine Goodsell (1844–1920) was the wife of Standard Oil co-founder William Rockefeller, Jr. (1841–1922).