Its county seat is Perth, which was first settled in 1816[2] and was known as a social and political capital before being overshadowed by a city known today as Ottawa.

[3] Most European settlements of the county began in 1816, when Drummond, Beckwith and Bathurst townships were named and initially surveyed.

[9] Effective January 1, 1850, Bathurst District was abolished, and the "United Counties of Lanark and Renfrew" replaced it for municipal and judicial purposes.

[12] The separation of Renfrew from Lanark began in 1861, with the creation of a Provisional Municipal Council[13] that held its first meeting in June 1861.

The landscape is varied including Canadian Shield (with gneiss, granite and marble) as well as limestone plains, with a variety of tills, sands and clays left from the melting of glaciers in the last ice age.

[16] The clearance of forests began with early settlement, at which time one of the important exports from the area was potash, made from the ashes of the trees burned in clearing.

Keddy's list adds areas such as Playfairville Rapids,[22] Lavant/Darling Spillway and the Carleton Place Hackberry stand.

[23] This shoreline was formed about 12,000 years ago near the end of the last ice age when much of the Ottawa Valley was inundated by the Champlain Sea.