Blacksod is of unusual design for a lighthouse, being an unpainted square block of a building with only a small conical lantern section on top, which is painted white.

A Lieutenant Nugent, an officer in the British Coastguard stationed at Belmullet, requested in a letter that a lighthouse be placed on Blackrock Island.

[3] But Inspector George Halpin, a senior civil engineer responsible for building Irish lighthouses, recommended to the Dublin Ballast Board (the predecessor to the Commissioners of Irish Lights) that a sea light should not be built on Blackrock Island but instead be sited on Blacksod Point – the southernmost point of the Mullet Peninsula – to guide vessels into Blacksod Bay.

[4] The lighthouse at Blacksod Point was completed in 1864; the work had been funded by Bryan Carey, one of the leading merchants in Belmullet at that time.

While remaining neutral during World War II, Ireland continued to supply weather reports to Britain under an agreement in place since independence.