Apex Mountain is an mountain summit located in Okanogan County in Washington state. It is part of the Okanogan Range which is a sub-range of the North Cascades and Cascade Range. The mountain is situated south of the Canada-United States border, on the east side of the Cascade crest, in the Pasayten Wilderness, on land managed by Okanogan National Forest. The nearest higher peak is Amphitheater Mountain, to the west-northwest. The Pacific Northwest Trail traverses the northern slopes of Apex Mountain as it crosses Apex Pass. Precipitation runoff from Apex Mountain drains west into Cathedral Creek, or east into Tungsten Creek, both tributaries of the Chewuch River.