It included the area which is now part of Canberra and as far north as Lake George and Yass.
A large area of the county was transferred to the Commonwealth government in 1909 in the Seat of Government Acceptance Act to make part of the Australian Capital Territory, along with land in Cowley County.
Part of the ACT border is determined by property boundaries in the Parish of Keewong, in the County of Murray; specifically the southern end of portions 177, 218, 211, 36, and 38.
The four parishes of Canberra, Yarrolumla, Narrabundah and Gigerline became part of the Australian Capital Territory in 1911.
Some of the other parishes are smaller than they were in the nineteenth century, due to land being taken out of them for the ACT; this includes Tuggeranong, Queanbeyan, Amungula, Pialligo, Goorooyarroo, Ginninderra and Weetangera.