The county is located 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.