The reserved land is located entirely on the north bank of the Great Whale River for a distance of approximately 43 km (27 mi).

The Cree reserved land includes the urbanized core of Whapmagoostui, which is also bordering that of Kuujjuarapik, like two neighbouring neighbourhoods of the same city.

Predictably, given its northern latitude, Whapmagoostui has a subarctic climate (Dfc) under the Köppen climate classification, but strongly modified by its location on the southeastern (predominantly windward) shore of Hudson Bay, particularly from May/June through November, the primary season when Hudson Bay's surface is unfrozen, i.e. open water.

Similar to a pattern evident in heavily "lake-influenced" areas around the U.S. Great Lakes (i.e. Holland and Sault Ste.

Marie, Michigan), in spring and early summer, water temperatures are cooler than those of surrounding land areas, encouraging low clouds and fog, but also stable conditions and less precipitation.

In fall and early winter, the pattern is reversed: water temperatures are warmer than those of surrounding land areas, encouraging cumulus cloud formation and unstable conditions, meaning low-pressure systems passing from cooler land to warmer water often intensify.

In Whapmagoostui, this pattern means average monthly precipitation peaks in September – when increasingly cold air masses passing eastward and southeastward across the open waters of Hudson Bay are warmed and destabilized by their over-water passage, producing thick clouds and frequent, often-heavy instability rain (and from October to December, snow) showers.

From late November into December, Hudson Bay freezes, and by January, its frozen surface provides little modification to Arctic air masses, and less moisture, i.e. snow, to Whapmagoostui.

Considering its marine position on the 55th parallel, the climate is extremely cold when compared with cities like Glasgow and Copenhagen in northern Europe and Chinook-affected areas further to the west in Canada's interior.

In 1940 the Cree were forced to give up their nomadic way of life when the American army opened a military air base here.