While Dillon was a federal judge, he wrote "Municipal Corporations" (1872), which was one of the earliest books to present the subject, and people still study it today. He was also the author of "Removal of Cases from State Courts to Federal Courts" and "Municipal Bonds", both in 1876. On February 17, 1876, Justice Dillon ruled Ulysses S. Grant's deposition for Orville E. Babcock was admissible in court during the Whiskey Ring graft prosecutions. After leaving the Circuit Court, Dillon was a professor at Columbia Law School from 1879 until 1882, where he taught real estate and equity. He then taught at Yale Law School from 1891 until 1892. While at Yale, he also was the president of the American Bar Association. Dillon then returned to private practice until his death in 1914 in New York City.