The area now known as Laois (pronounced "Leesh") was originally inhabited by the O'Mordha Clan (later known as O'More and then Moore). In ancient times the O’More tribe-name of Ui Laoighis (Pronounced Leesh) was applied to their territory, and that it is derived from a famous Ulster ancestor named Lughaidh Laeighseach (Lewy Leesagh), son of Laeighseach Canvore, son of the renowned Conall Cearnach, chief of the Red Branch Knights of Ulster in the first century.
The county itself was created in 1556 by Mary I of England as Queen's County, Laois received its present Irish language name following the Irish War of Independence. Portlaoise (previously Maryborough) is the county town.
Laois was the subject of two Plantations or colonizations by English settlers. The first occurred in 1556, when the Earl of Sussex dispossessed the O'More clan from the area and attempted to replace them with English settlers. However, this only led to a long drawn out guerilla war in the county and left a small English community clustered around garrisons. There was a more successful plantation in the county in 17th century, which expanded the existing English settlement with more landowners and tenants from England. Neither plantation was fully successful due to a lack of tenants and because of continuous raids and attacks by the O'Mores.
Finally, the county became home to a community of French Huguenots in the 1690s, who were settled in Ireland after their service to William of Orange in the Williamite war in Ireland. In addition to this, large numbers of Quakers settled in Mountmellick and developed the area.
The population of County Laois is expanding rapidly, given its easy commute to Dublin and affordable housing in pleasant surroundings. In the 2006 census the population had increased by 14% to 67,000 people.
The county is landlocked and, uniquely amongst Irish counties it does not border any other counties with a sea coast. It is therefore considered to be "the most landlocked county in Ireland"
Laois lies one hour southwest of Dublin, with train stations at Portlaoise, Portarlington and Ballybrophy. Irish Rail  runs eighteen trains to and from these stations a day, with further connections to Galway and the west of Ireland, Limerick and Cork.