3rd (County Down) Battalion, Ulster Defence Regiment (3 UDR) was formed in 1970 as part of the seven original battalions specified in The Ulster Defence Regiment Act 1969, which received Royal Assent on 18 December 1969 and was brought into force on 1 January 1970. It was, along with the rest of the regiment, amalgamated with the Royal Irish Rangers in 1992 to form the Royal Irish Regiment.