In 1837 the village of Sydenham was surveyed by Charles Rankin, P.L.S. In 1856 it was incorporated as the Town of Owen Sound with an estimated population of 2,000.
Grey County was created in 1852 and named in honour of the British Colonial Secretary's father, Charles Grey, 2nd Earl Grey, who was Prime Minister of the United Kingdom from 1830-1834. In 1861-1862 the first gravel roads were constructed into Owen Sound at a cost of $300,000. The four roads graveled were The Garafraxa Road running from Fergus to Owen Sound (now Highway 6); the Durham Road leading east and west from the village of Durham (now County Road 4); the Lake Shore Road from Collingwood to Owen Sound (now Highway 26) and the Toronto and Sydenham Road leading from Toronto to Owen Sound (now Highway 10). Prior to the road building it often took two days to walk up to Owen Sound.
On January 1, 2001, Grey County underwent a major reorganization. The majority of towns, villages, and townships were amalgamated, reducing the number of municipalities from 26 to 9. Only Owen Sound and Hanover were unaffected.