Offaly lies near the centre of Ireland. In the south-east of the county are the Heathery Slieve Bloom Mountains, among which there are pretty valleys to be explored. The rest of the county is largely level plain and bogland, with occasional elevations. In the west the River Shannon separates the county from Counties Galway and Roscommon. There are numerous points of interest in the towns and countryside of Offaly, including one of the most important historic sites in Ireland - Clonmacnois.
The width of the county is crossed by the Grand Canal. Danish raths, or hill fortresses, and remains of ancient churches and monasteries are among the points of interest. Part of the kingdom of Offaly in ancient Ireland, the area was known as King's County from 1556 until the Irish Free State was established in 1922.