A number of original Irish names have been anglicised as "Connolly." The Ó Conghalaigh, from conghal, "as fierce as a wolf", were based in Connacht, where the English version is now often spelt "Connelly", or "Conneely"; the name arose as Ó Coingheallaigh in West Cork, while Ulster Connollys derive from both the Ó Conghalaigh of Fermanagh, who gave their name to Derrygonnelly, "Connolly's oakwood", and the Monaghan Connollys, for whom a number of separate origins are suggested, as a branch of the southern Uí Neill, or as a branch of the MacMahons. Whatever their origin, the Monaghan family have been the most prominent of the Connollys. They are first noted as coming to prominence in the fifteenth century and are recorded as having "Chiefs of the Name" up to the seventeenth century. They were instrumental in organising the native Irish rebellion of 1641 and, following its failure, lost their power and possessions.
In 1890 the surname was 23rd most common in Ireland, with 381 births of the name, mostly in Ulster. By 1996, the ranking had slipped to 33rd. The variant Conneely was found exclusively in Connacht in 1890, with most occurrences in Co. Galway.
.Speaker William Connolly (1662-1729) was a member of the Monaghan branch, though born in Ballyshannon, Co. Donegal. He amassed enormous wealth by dealing in the property confiscated from the native landowners after the defeat of James II at the Battle of the Boyne. He became a pillar of the Anglo-Irish establishment, holding the Speakership of the Irish House of Commons among other appointments. He is best remembered now for Castletown House, the magnificent Palladian mansion he had built in Co. Kildare.
. Also of the Monaghan family was the rather different James Connolly (1870-1916), founder of Irish socialism. Born of Irish emigrant parents in Edinburgh, he came to Ireland in 1913 as a full-time labour organiser and agitator, founded a worker’s militia, the Citizen Army, and threw in his lot with the nationalist revolutionaries of 1916. His writings have become classics of socialist theory.