Tahtlum Peak is a mountain summit located east-southeast of Chinook Pass in the William O. Douglas Wilderness. It's situated north of Dewey Lake in Yakima County of Washington state. Tahtlum Peak is part of the Cascade Range and its nearest higher neighbor is Dewey Peak, to the south. The name tahtlum derives from Chinook Jargon which means ten. Precipitation runoff from Tahtlum Peak drains into tributaries of the Yakima River.