Birr is a town in County Offaly, Ireland. Between 1620 and 1899 it was called Parsonstown, after the Parsons family who were local landowners and hereditary Earls of Rosse. Birr is a designated Irish Heritage Town with a carefully preserved Georgian heritage. Birr itself has graceful wide streets and elegant buildings. Many of the houses in John's Place and Oxmantown Mall have exquisite fanlight windows of the Georgian period. The town is known for Birr Castle and gardens, home of the Parsons family, and also site of the Leviathan of Parsonstown, the largest telescope in the world for over 70 years, and a large modern radio telescope.