The name Dillon is an English given name derived from the Gaelic surname Ó Duilleáin, meaning "descendant of Duilleán". Duilleán itself is a diminutive of the Irish word duilleog, meaning "leaf" or "folio". The name likely originated in Ireland as a descriptive surname for a family associated with leaves or foliage.

The earliest recorded use of the name Dillon can be traced back to the 12th century in Ireland. It was initially a surname borne by an influential family of Norman descent who settled in County Westmeath. The family's ancestral seat was at Dillon's Grove near Kilcormac.

One of the earliest notable figures with the name Dillon was Sir Henry Dillon (1277-1344), an Irish nobleman and military commander who served as Lord Chancellor of Ireland during the reign of Edward III. He played a significant role in the Anglo-Norman conquest of Ireland and was granted extensive lands in County Meath.

In the 16th century, James Dillon (1572-1648) was an Irish Catholic lawyer and landowner who served as Chief Justice of the Irish Common Pleas. He was a prominent figure in the Irish Rebellion of 1641 and was later executed for his involvement.

Another notable figure was Arthur Dillon (1670-1733), a French-born Irish general who served in the French army during the War of the Spanish Succession. He was a member of the Jacobite Irish Brigade and played a crucial role in several battles against the English.

During the American Revolutionary War, Theodorick Bland Dillon (1733-1776) was an officer in the Continental Army. He served under General George Washington and was killed in action during the Battle of White Plains in 1776.

In the 19th century, John Dillon (1851-1927) was an Irish nationalist politician and a prominent leader of the Irish Parliamentary Party. He advocated for Irish home rule and played a significant role in the Irish independence movement.

The name Dillon has a rich history and has been borne by many notable figures throughout the centuries, particularly in Ireland and among the Irish diaspora. Its origins as a descriptive surname and its association with influential families and historical events have contributed to its enduring popularity as a given name.