Rainy River District is a district and census division in Northwestern Ontario in the Canadian province of Ontario. It was created in 1885. It is the only division in Ontario that lies completely in the Central Time Zone, except for the township of Atikokan observing Eastern Standard Time for part of the year. Its seat is Fort Frances. It is known for its fishing and its location on the US border opposite International Falls, Minnesota, and Baudette, Minnesota.

Northwestern Ontario is a secondary region of Northern Ontario in the Canadian province of Ontario which lies north and west of Lake Superior and west of Hudson Bay and James Bay. It includes most of subarctic Ontario. Its western boundary is the Canadian province of Manitoba, which disputed Ontario's claim to the western part of the region. Ontario's right to Northwestern Ontario was determined by the Judicial Committee of the Privy Council in 1884 and confirmed by the Canada Act, 1889, of the Parliament of the United Kingdom. In 1912, the Parliament of Canada by the Ontario Boundaries Extension Act gave jurisdiction over the District of Patricia to Ontario, thereby extending the northern boundary of the province to Hudson Bay.