The official definition of the R819 from the Roads Act 1993 (Classification of Regional Roads) Order 2006 states:[2][3]
R819: Long Mile Road - Tallaght, County Dublin
Between its junction with R110 at Long Mile Road in the city of Dublin and its junction with N81 at Tallaght Bypass in the town of Tallaght in the county of South Dublin via Walkinstown Road in the city of Dublin: and Greenhills Road in the county of South Dublin.