Birr Castle is a large castle

Castle

A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...

 in the town of Birr

Birr

Birr is a town in County Offaly, Ireland. Once called Parsonstown, after the Parsons family who were local landowners and hereditary Earls of Rosse. It is also a parish in the Roman Catholic Diocese of Killaloe....

 in County Offaly

County Offaly

County Offaly is a county in Ireland. It is part of the Midlands Region and is also located in the province of Leinster. It is named after the ancient Kingdom of Uí Failghe and was formerly known as King's County until the establishment of the Irish Free State in 1922. Offaly County Council is...

, Ireland

Republic of Ireland

Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

. It is the home of the seventh Earl of Rosse

Earl of Rosse

Earl of Rosse is a title that has been created twice in the Peerage of Ireland, both times for members of the Parsons family. It is not to be confused with the Scottish title of Earl of Ross. The Parsons family were originally an English family of which five brothers settled in Ireland during the...

, and as such the residential areas of the castle are not open to the public, though the grounds and gardens of the demesne

Demesne

In the feudal system the demesne was all the land, not necessarily all contiguous to the manor house, which was retained by a lord of the manor for his own use and support, under his own management, as distinguished from land sub-enfeoffed by him to others as sub-tenants...

 are publicly accessible.
The castle grounds are also home to Ireland's Historic Science Centre, a museum of Ireland's historic scientists and their contributions to astronomy and botany.
There has been a castle on the site since 1170, and from the 14th to the 17th century the O'Carroll

O'Carroll

O' Carroll is an Irish family name, deriving from the Gaelic Ó Cearbhail.-O' Carroll name and territorial extent:Notable is the history of the Clan Ó Cearbhail whose territory, known as Ely O' Carroll in Éile, consisted of the pasture lands of Ballycrinass, Rosscullenagh and Drumcan, extending to...

 family ruled from here over an area known as "Ely O'Carroll".

After the death of Sir Charles O'Carroll, Sir Laurence Parsons was granted Birr Castle and 1277 acres (5.2 km²) of land in 1620.