For most of the medieval period, Dungannon was simply where the O'Neills lived - the Gaelic dynasty that ruled much of Ulster from this hilltop. Their stewards, the O'Hagans, presided over the inauguration ceremonies at Tullyhogue Fort, an Iron Age mound four miles to the northeast, where each new O'Neill chief was raised to power on a stone chair. After the Nine Years' War ended in defeat, ninety-nine Irish chieftains, Hugh O'Neill among them, sailed from Rathmullan in 1607 and never came back. The Flight of the Earls broke a thousand years of Gaelic rule in a single tide. The English Crown confiscated their lands and handed Dungannon to Sir Arthur Chichester, the Lord Deputy of Ireland. By 1636, where the O'Neill kings had once held court, the Royal School Dungannon was teaching the sons of new settler families.

In February 1782, delegates from 147 Volunteer corps - Protestant militias originally raised against a French invasion - assembled at the Presbyterian church on Scotch Street. They arrived in uniform, armed, and increasingly convinced that the British Parliament had no right to legislate for Ireland. Taking on, as one observer put it, "the substance of a national assembly," they resolved that Westminster's claim to overrule the Irish Parliament was "unconstitutional" and "illegal." The Dungannon Convention helped force the concession of Irish legislative independence later that same year. A small Tyrone town had, for a moment, set the political weather for an entire country. Two further conventions followed in 1783 and 1793, and emigrants from these same congregations carried the name with them to the Appalachian foothills, where they founded Dungannon, Virginia.

By the early nineteenth century, Market Square thrummed every Thursday with bleachers' buyers from Belfast, who took their places on raised wooden "standings" while farmers brought webs of unbleached linen woven by their own families. A surveyor in 1802 called Dungannon "inferior to no other" Northern Ireland town for its progress in building. But progress had limits. In 1842, the Dungannon Workhouse opened on what is now the South Tyrone Hospital grounds, and through its doors over the next century passed about a thousand people - including, during the worst Famine years, young women shipped from this town to Australia between 1848 and 1850. They are remembered today as the Irish Famine Orphan Girls, and the memorial on the site simply honours "all those who sought shelter" within its walls.

On 24 August 1968, Northern Ireland's first civil rights march set out from Coalisland and ended in Dungannon. The local Campaign for Social Justice, founded by Councillor Patricia McCluskey and her husband Conn, a Dungannon GP, had been documenting Catholic exclusion from public housing for years. Seventeen families had already squatted at Fairmount Park in protest. The rally was officially banned. It happened anyway, peacefully. Less peaceful was what followed in the next decade. In March 1976, an Ulster Volunteer Force car bomb tore through the Hillcrest Bar on Donaghmore Road during St Patrick's Day celebrations, killing four civilians - two of them thirteen-year-old boys standing outside - and injuring nearly fifty more. In December 1979, a Provisional IRA land mine on the Ballygawley Road killed four British soldiers. Almost fifty people died in the Dungannon district during the Troubles.

Walk down Scotch Street today and you might hear Portuguese before you hear English. Moy Park, the poultry processor, is the largest employer in town, and the food-processing industry that grew up here in the late twentieth century reached out for workers wherever it could find them - to Portugal first, then through Portuguese-speaking networks to Brazil, Mozambique and East Timor. By the 2021 census, over a third of Dungannon's 16,282 residents had been born outside the British Isles, the highest such proportion of any town in Northern Ireland. The 2023 council elections returned a nationalist majority in the Dungannon electoral area for the first time. The hilltop that watched seven counties is now lived in by people from a half-dozen of them - and from far beyond.

In 2007, the Channel 4 archaeology programme Time Team partially excavated Castle Hill, uncovering moat and wall fragments of the fortress Hugh O'Neill had burned four centuries earlier. The dig confirmed what local memory had always preserved: that this small rise of ground had been, for a very long time, the place from which Ulster was watched, claimed and lost. The skyline today is dominated not by walls but by the spires of St Patrick's, St Anne's and the Presbyterian church tower, with the old greenway running through the trackbed of the long-closed Derry Road station. It is a town that has been rebuilt, repeatedly, on top of itself - and the hill is still here, still visible from anywhere on the surrounding plain.