This study aims to provide an overview of major population, employment, social composition, and urban concentration trends since 1871 in the region now called "Northern Ontario" (or "Nord de l'Ontario" or "Ontario-Nord"). The study pays special attention to the pattern of decline in population and employment that has been occurring in the last several decades not only in aggregate, but also at the district and community levels. The study raises some structural issues of economic development underlying the labour market and distributional disparities described as well as discusses certain measurement issues particularly related to economic dependency.[A1] More detailed analysis of the economic conditions of decline is beyond the present task. Nor is the study focused on immediate policy issues but rather on contributing to a deeper empirical basis for policy discussion. To heighten the importance of the larger trends treated here for policy, the study will refer to some aspects of current dominant policy thinking, such as in the Province's Growth Plan for Northern Ontario (2011) and some publications of the provincially funded Northern Policy Institute. The early development of Northern Ontario occurred in the context of a vast Canadian colonial expansion in territory and settlement westward and northward, particularly following Canadian transcontinental railway development from the 1880s. As established at Confederation (1867), the then province of Ontario occupied a smaller territory of about 263, 000 km2 above the St Lawrence River and Lakes Ontario, Erie, Huron, and Superior (Map 1).

But by 1912, when Ontario's boundaries reached their current limits, the province had more than tripled its size to over 900, 000 km2, most being through colonial expansion into Northern Ontario. This territorial and settlement expansion was based mainly in southern Ontario and grew out of its earlier colonization. Northern Ontario came to cover approximately 87 percent of the land area of Ontario (Table 2 data). Typical of settler colonial place-naming patterns, the area was also called "New Ontario" (or "Nouvel-Ontario") . This study uses the term "Northern Ontario" (or "Nord de l'Ontario") reflecting more contemporary common terms. The process of defining the region of Northern Ontario has been a matter of contention. For purposes of the present study, we need to address particularly the issue of the southeastern boundary, which has been imposed in different forms for purposes of governmental administration and programs, and never negotiated with Indigenous peoples. There is wide acceptance that today Northern Ontario includes at least nine territorial districts : Algoma, Cochrane, Kenora, Manitoulin, Nipissing, Rainy River, Sudbury, Thunder Bay, and Timiskaming.

For official statistical purposes, these unincorporated districts are also census divisions , except for Sudbury, which has been divided into two census divisions (Sudbury District and Greater Sudbury), thus making ten census divisions (Map 2).[2] This ten-census division definition of Northern Ontario is fairly consistent with much popular discussion which takes the southernmost boundary to be the westward-flowing French River, from its mouth on Lake Huron (Georgian Bay) through to Lake Nipissing then to the eastward-flowing Mattawa River from North Bay through to Mattawa on the Ottawa River.