The official definition of the R829 from the Roads Act 1993 (Classification of Regional Roads) Order 2012 states:[2]
R829: Monkstown - Dalkey, County Dublin
Between its junction with R119 at Monkstown Road and its junction with R119 at Hyde Road Dalkey via Carrickbrennan Road, Mounttown Upper, Mounttown Lower, Glenageary Road Upper and Barnhill Road all in the county of Dún Laoghaire–Rathdown.