Tully is a relaxed, rarely used Irish surname possibility. Sources disagree on the meaning, depending on what root is used. The Irish tulach means hill or mound, while tuile means flood. Other sources relate it to the Roman Tullius, most notably the name of the philosopher Marcus Tullius Cicero, sometimes anglicized as Tully. Statesman Alexander Hamilton used the pen name Tully when he wrote editorials denouncing the instigators of the Whiskey Rebellion.
The ancient Irish name Tuathal, which is translated as Tully, was given to many Irish kings and heroes.