James Samson, a Scottish immigrant, purchased 7,367 acres (2,981 ha) of land in the area in 1852. Samson built a general store and tavern along the Owen Sound Road (now Highway 6), and named the settlement after his hometown of Cumnock, Scotland.[6][7] A post office was established in Samson's store in 1855, with Samson as postmaster.[8]
In 1855, Richard Gluyas laid out Gluyasville a short distance north of Cumnock. Gluyasville was eventually absorbed by Cumnock.[7]
The Wellington, Grey and Bruce Railway built a line through Cumnock in 1871, and a station was built there.[9][10] That same year, Cumnock was noted as having a saw mill, a wagon maker, and two hotels (the British Hotel and the Red Lion).[10] The Red Lion Hotel was owned by Scottish immigrant John Muir, who "went back to Scotland several times to bring back wives to Cumnock".[6]
The Cumnock Methodist Church was built in 1877.[11]
Cumnock was noted as having a cheese factory in 1880.[12]
At its peak, Cumnock had a population of 200, though by 1908, the settlement had one hotel, two stores, two churches, and a population of 86.[6][13]
The post office closed in 1915, and the Methodist church closed in 1924.[8][11]
An author writing in 1933 described the northern boundary of Nichol Township "where Cumnock used to be",[14] and by 1969, Cumnock was no longer listed on provincial maps.[6]
In 1964, the County of Wellington purchased two parcels of forested land at Cumnock for recreational use. Located within the westernmost parcel is the Cumnock Tract, a 1.5 km (0.93 mi) walking trail.[15]