When Dennis Ennis was born on 20 March 1788, in Charlestown, Washington, Rhode Island, United States, his father, Paul Enos Ennis, was 34 and his mother, Mary Hannah Webster, was 28. He married Mary Crandall on 30 April 1813, in Charlestown, Washington, Rhode Island, United States. They were the parents of at least 8 sons and 5 daughters. He died on 24 December 1867, in Richmond, Washington, Rhode Island, United States, at the age of 79, and was buried in Charlestown, Washington, Rhode Island, United States.