Mountaindale is an unincorporated community in Washington County, Oregon, United States, about four miles northwest of North Plains.

[2] Settled in the 1850s, the small community was the longtime home of the Mountaindale Store.

[3] The Atfalati tribe of Native Americans had a seasonal campsite in the area prior to the arrival of European-Americans in the 1830s.

[5] Mountaindale School District 41 was formed on December 5, 1868, with Alzada Cornelius as the first teacher and W. D. Pittenger as the first superintendent.

[7][8] The name combining "mountain" and "dale" is descriptive, as the community is where East Fork Dairy Creek emerges from the foothills at the north edge of the Tualatin Valley.