In 1872, President Ulysses S. Grant appointed John Thornton to the US Marine Corps. He was assigned to the Charlestown Navy Yard in Boston.
He later served in Pensacola, Florida and at Annapolis. As a second lieutenant, he served with the Mediterranean Fleet under Admiral Worden. While stationed at Nice, France, he met Jessie Willis, daughter of composer Richard Storrs Willis and niece of poet Nathaniel P. Willis. They married on March 12, 1877, in New York City.
John Thornton was responsible for bringing home from Spain fugitive Tammany chief "Boss" Tweed to New York. He also led a regiment to break the strike of railroad workers in Pennsylvania.
By 1878, he and Jessie had started a family. He turned down an assignment to China and resigned his commission to remain with his family, which was living in Washington, D.C. By 1881, the family returned to Detroit and John established a business in real estate.
John Thornton and Jessie had six children. The first child was Jessie Willis (1878-1906). She married Rob Leicester Wagner (1872-1942), an artist, journalist and filmmaker. She died in Santa Barbara, Calif.
The second child was a son. Thornton (m. Elsie Moran) was a commander in the Michigan Naval Militia and saw action at San Juan during the Spanish-American War. Daughter Archange Macomb was unmarried. A second son, John "Jack" (m. Dorothy Farrish), owned a Ford dealership in St. Louis. Daughter Alexandrine Cairns married Duncan McNabb. The youngest child was Willis, who joined Jack in St. Louis to help run the car dealership.
John Thornton died of pneumonia at his home at 597 Jefferson Ave.