Global Range: Aase's onion is endemic to southwestern Idaho, occurring in the foothills around Boise and arcing northwest to near Emmett, an aerial distance of approximately 18 miles. In the Boise Foothills, the easternmost populations are known from the Hulls Gulch and lower Cottonwood Creek areas, while the Freezeout Hill vicinity near Emmett contains the westernmost foothill populations. Disjunct populations have recently been confirmed from near the towns of Payette and Weiser, northwest of the species main range. Populations previously reported from the Danskin Mountains, east of Boise are really Allium simillimum. Populations are located in Ada, Boise, Gem, Payette, and Washington Counties.