Lanark County is a county located in the Canadian province of Ontario. Its county seat is Perth, which was first settled in 1816. Most European settlements of the county began in 1816, when Drummond, Beckwith and Bathurst townships were named and initially surveyed. The first farm north of the Rideau was cleared and settled somewhat earlier, in 1790. The county took its name from the town of Lanark in Scotland. Nearly all the townships were named after British public and military figures from the era of early settlement
The county is in the sub-region of Southern Ontario named Eastern Ontario. Geologically, the northern part of the county is in the Canadian Shield and the southern part is in the Great Lakes Basin. The county has two large rivers, the Mississippi and Rideau, each of which empty into the Ottawa River. 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. At the time of settlement, most of the county was covered in temperate deciduous forest; the dominant forest trees included maple, hemlock, oak, and beech. Some of the higher ridges in the west of the county were likely once natural fire barrens, with distinctive fauna and flora. The clearance of forests began with the early settlement, at which time one of the important exports from the area was potash, made from the ashes of the trees burned in the clearing.
The county is one of the top centres of maple syrup production in Ontario and describes itself as "The Maple Syrup Capital of Ontario"
There are two provincial parks in Lanark County: Murphy's Point Provincial Park on Big Rideau Lake and Silver Lake Provincial Park along Highway 7 near the west end of the county. The Rideau Trail and Trans-Canada Trail both go through Lanark County. There are also several conservation areas run by the Mississippi Valley Conservation Authority, the Rideau Valley Conservation Authority, and the Mississippi Madawaska Land Trust. The K&P rail trail goes through the northwest corner of the county. The natural diversity of the landscape supports over 1,200 species of plants in the county flora. Seventeen areas have been documented as outstanding examples of plant diversity; these include Blueberry Mountain, Burnt Lands Alvar, Clay Bank Alvar, Christie Lake, Murphy's Point Provincial Park and Almonte Town Park. The county also has 47 provincially significant wetlands. Some of the largest are Blueberry Marsh (north of Perth), the Innisville Wetlands (upstream of Mississippi Lake) and the Goodwood Marsh south of Carleton Place. In addition to David White's list of 17 areas of plant diversity, Paul Keddy lists 17 special places in the county. Both lists have the Burnt Lands Alvar, the Christie Lake Barrens and Murphy's Point Provincial Park. Keddy's list adds areas such as Playfairville Rapids, Lavant/Darling Spillway, and the Carleton Place Hackberry stand. Also of interest is an old shoreline that crosses the county diagonally, approximately from Almonte in the northeast to Perth in the southwest. 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. Many areas below this old shoreline are flat clay plains, with occasional outcrops of gneiss or limestone ridges.