Salt Island Lighthouse, located on the Holyhead Mail Pier, was designed in 1821 by engineer John Rennie. It replaced an earlier tower, of which very little is known.
The lighthouse is thought to be the second oldest lighthouse in Wales; the oldest being Point of Ayr Lighthouse.
Holyhead Harbour was the terminal for mail packets to and from Dublin. An identical tower was also built at Howth in Ireland for the terminal of the Irish packet.
A gas works located on the island powered the lighthouse and piers.
Following the opening of a new harbour in 1873 and the establishment of the Holyhead Breakwater lighthouse, Salt Island Lighthouse was decommissioned.