Blackrock Lighthouse was built in 1864 from stone quarried directly out of the rock it stands on. The fifty-foot circular tower attaches to a single-storey keepers' dwelling; both are painted white against the dark basalt. It is one of the most remote lighthouses in Ireland and the most westerly off the Mayo coast. For twenty-nine years after construction, keepers and their families lived full-time on the rock - a category of existence so isolated that the British government eventually decided it could not be asked of people indefinitely. In 1893 the station became 'relieving': keepers were rotated out from new dwellings built at Blacksod on the mainland, with relief shifts of weeks rather than years. The light was automated in 1974, and the island became uninhabited. In 1999 the lighthouse was converted to solar power.

In the winter of 1942-43, during the Emergency in Ireland's neutral wartime, the routine of ten-day relief broke down completely. Storms destroyed the landing stage and the derricks used to swing supplies ashore. Three lighthouse keepers - Walter Coupe, Michael O'Connor, and principal keeper Jack Scott - were stranded on Blackrock with rations already reduced by wartime shortages. Captain John Padden of the Irish Lights tender made repeated attempts in dangerous seas; on a few occasions, supply baskets were successfully thrown across to the rock. On 17 February 1943, finding a brief lull in the weather, Padden was able to bring off Coupe (who had been on the rock for 117 days) and O'Connor (about 90 days). Scott, the principal keeper, stayed on to direct the rebuilding of the landing infrastructure. The siege of Blackrock Lighthouse became part of the folk memory of the Mayo coast.

On 20 August 1940, with Ireland officially neutral but the Battle of the Atlantic raging just offshore, a German bomber attacked the SS Macville as the cargo ship passed close to Blackrock Island. The aircraft also damaged the lighthouse itself - several panes of the lantern were broken and the roof took hits. It was a small incident in a vast war, but it underlined the fact that even Ireland's most distant inhabited outposts could not entirely escape the conflict. The Macville survived the attack; the lighthouse was repaired and continued to operate.

On 14 March 2017, Blackrock Island became the site of a different kind of tragedy. Rescue 116, a Sikorsky S-92 of the Irish Coast Guard, struck the island in the early hours of the morning while approaching Blacksod to refuel. All four crew - Captain Dara Fitzpatrick, Chief Pilot Mark Duffy, winch operator Paul Ormsby, and winch man Ciaran Smith - were lost. The recovery of the helicopter and the search for the missing crew faced exactly the difficulties that had defined life on Blackrock for over a century: heavy seas, sudden weather, the rock's geometry breaking up swells and currents in unpredictable ways. The Irish Lights vessel Granuaile, which now bears the name of Mayo's pirate queen, was among the ships involved in the recovery.

The seabed off Blackrock drops away quickly - 40 metres within a kilometre of the island, deeper toward Achill. The Blackrock fishing grounds attract serious sea anglers chasing blue shark, porbeagle, halibut, and bluefin tuna. A small islet sits 125 metres to the east, with about five more rocky outcrops - Fish Rock, Carrickaduff, Carrackabrown - scattered for a couple of kilometres west of the lighthouse. Seabirds nest where they can find a foothold; the rock is too steep and too lashed by spray for much else to take root. From the Mullet Peninsula on a clear day, Blackrock looks small and almost picturesque on the western horizon. Up close it is enormous, dark, and entirely indifferent.