Grande Prairie (Fr. gräNd prâˌrēˈ) [key], city (1991 pop. 28,271), W Alta., Canada, NW of Edmonton. It is the chief business center for the Peace River valley farming area. The discovery of oil and natural gas in the region in the late 1970s led to a short boom which dramatically increased the city's population. The Northern Winter Carnival is held in the city annually.