I often hear people say that their ancestors were from a particular province. For the budding family historian, this is often announced with some pride as if they know where their ancestors were from. Then I inform them that provinces are regions. However, the name of the province is a start.
Historically, Ireland is divided into the provinces of Connaught, Leinster, Munster, and Ulster. Present-day Northern Ireland encompasses most of Ulster except for the three counties of Cavan, Donegal, and Monaghan, which are part of the Republic of Ireland. Ulster can be particularly confusing for the beginner. The provinces and counties within each are as follows:
Connaught: Galway, Leitrim, Mayo, Roscommon, Sligo
Leinster: Carlow, Dublin, Kildare, Kilkenny, Leix (Queens), Longford, Louth, Meath, Offaly (Kings), Westmeath, Wexford, Wicklow
Munster: Clare, Cork, Kerry, Limerick, Tipperary, Waterford
Ulster: Antrim, Armagh, Cavan, Donegal, Down, Fermanagh, Londonderry (Derry), Monaghan, Tyrone
I commonly see the province names in published family history books, online pedigrees, military pension records, and sometimes in church registers. The most common ones are Ulster and Connaught as they have traumatic histories which stick out in family lore. While Presbyterian immigrants did not always come from Ulster, the vast majority of them did. This in effect narrows down that province as the most likely candidate from which to begin that search. So many Irish Catholics were traumatized by the Potato Famine and poverty in Connaught that the very name has an emotional component attached to it. I seldom hear Leinster and Munster passed down.
If you see one of the four provinces in a record it does provide you with a guide in your research. This can be especially helpful with common surnames.