In the 14th century the O'Neills built a castle on what is today known as Castle Hill; the location was ideal for a fort as it was one of the highest points in the area, and dominated the surrounding countryside with the ability to see seven counties depending on the weather.This castle was burned in 1602 by Hugh O'Neill, 2nd Earl of Tyrone as Crown forces under Lord Mountjoy closed in on the Gaelic lords towards the end of the Nine Years' War.
On 24 August 1968, the Campaign for Social Justice (CSJ), the Northern Ireland Civil Rights Association (NICRA), and other groups, held Northern Ireland's first civil rights march from Coalisland to Dungannon.
For centuries, it was the 'capital' of the O'Neill dynasty, who dominated most of Ulster and built a castle on the hill.
After the O'Neills' defeat in the Nine Years' War, the English founded a plantation town on the site, which grew into what is now Dungannon.
In 1641 after seizing the town in the opening stages of the Irish Rebellion, Sir Phelim O'Neill issued the Proclamation of Dungannon in which the rebels set out their aims and proclaimed their loyalty to Charles I.
O'Neill hinted that they had been ordered to rise by the King and later produced a commission which he claimed Charles had issued to him.