Northern Ontario is a primary geographic and quasi-administrative region of the Canadian province of Ontario, the other primary region being Southern Ontario. Most of the core geographic region is located on part of the Superior Geological Province of the Canadian Shield, a vast rocky plateau located mainly north of Lake Huron (including Georgian Bay), the French River, Lake Nipissing, and the Mattawa River. The statistical region extends south of the Mattawa River to include all of the District of Nipissing. The southern section of this district lies on part of the Grenville Geological Province of the Shield which occupies the transitional area between Northern and Southern Ontario. The extended federal and provincial quasi-administrative regions of Northern Ontario have their own boundaries even further south in the transitional area that vary according to their respective government policies and requirements. Ontario government departments and agencies such as the Growth Plan for Northern Ontario and the Northern Ontario Heritage Fund Corporation define Northern Ontario as all areas north of, and including, the districts of Parry Sound and Nipissing for political purposes, while the federal government, but not the provincial, also includes the district of Muskoka.
The statistical region has a land area of 806,000 km2 (310,000 mi2) and constitutes 88 per cent of the land area of Ontario, but with just 780,000 people it contains only about six per cent of the province's population. The climate is characterized by extremes of temperature, extremely cold in winter and hot in summer. The principal industries are mining, forestry, and hydroelectricity.
For some purposes, Northern Ontario is further subdivided into Northeastern and Northwestern Ontario. When the region is divided in this way, the three westernmost districts (Rainy River, Kenora and Thunder Bay) constitute "Northwestern Ontario" and the other districts constitute "Northeastern Ontario." Northeastern Ontario contains two thirds of Northern Ontario's population.
In the early 20th century, Northern Ontario was often called "New Ontario", although this name fell into disuse because of its colonial connotations. (In French, however, the region may still be referred to as Nouvel-Ontario, although le Nord de l'Ontario and Ontario-Nord are now more commonly used.)