[9][better source needed] The town's English name, Holyhead, has existed since at least the 14th century.

[10] Prior to the influence of the fort on the name, the hamlets which came before it were likely known as Llan y Gwyddel ('church/parish of the Irish') and Eglwys y Beddi ('church of the graves').

The Romans also built a watchtower on the top of Holyhead Mountain inside Mynydd y Twr, a prehistoric hillfort.

[12] Settlements in the area date from prehistoric times, with circular huts, burial chambers and standing stones featuring in the highest concentration in Britain.

Holyhead Central Conservation Area covers the historic Old Town core that developed around the Roman Fort.

[15] In the early nineteenth century, it was still undecided which port would be chosen as the primary sea link along the route from London to Dublin: Porthdinllaen, on the Llŷn Peninsula, or Holyhead in Anglesey.

It was also a transit point for British owners of multinational estates visiting their 'other lands' or London houses.

Key improvements made after the 1800 Act of Union with Ireland included the illumination of the South Stack Lighthouse in 1809, the construction of a built-up harbor in 1810, and the addition of a substantial breakwater between 1848 and 1873.

Although mail service through Holyhead was temporarily suspended in 1838 in favour of rail transport through Liverpool, the development of the north Wales coastal railway in 1850 led to its reinstatement.

The A5 terminates at Admiralty Arch (1822–24), which was designed by Thomas Harrison to commemorate a visit by King George IV in 1821 en route to Ireland and marked the zenith of Irish Mail coach operations.

Avanti West Coast runs direct trains to London Euston via Crewe[20] and Transport for Wales operate direct trains to Cardiff and Birmingham International, via Wrexham and Shrewsbury; they also operate on the route to Manchester Piccadilly, via Warrington.

[21] The rail and ferry terminals are connected (for pedestrians and cyclists) to the town centre by The Celtic Gateway bridge.

[6] In 2001, work was completed on the extension of the A55 North Wales Expressway from the Britannia Bridge to Holyhead, giving the town a dual carriageway connection to North Wales and the main British motorway network.

A large jetty in the harbour received ships from Jamaica and Australia, and their cargoes of alumina were transported on a rope-driven conveyor belt running underneath the town to the plant.

[26] The plant relied for its electricity supply on Wylfa nuclear power station, near Cemaes Bay.

[27] On 18 October 2010, the British government announced that Wylfa was one of the eight sites it considered suitable for future nuclear power stations.

[30] Like the rest of Wales and the British Isles, Holyhead has a maritime climate (Cfb according to the Köppen climate classification) with cool summers and mild winters, and often high winds exacerbated by its location by the Irish Sea.

The nearest official weather observation station is at RAF Valley, about five miles (eight kilometres) southeast of the town centre.

[38] Holyhead Town Hall was completed in 1875 and served as both a public events venue and meeting place for the local board and the urban district council which replaced it.

[48] Holyhead was officially twinned with Greystones, County Wicklow on 20 January 2012, and this is celebrated on a new road sign.