Fungi in the genus Armillaria are associated with an important disease of deciduous and coniferous trees and shrubs in western North America. This study examined the distribution of Armillaria by forest habitat types on the Kaibab National Forest and northern Coconino National Forest, Arizona. Over 400 trees were examined for Armillaria in 76 Interior West Forest Inventory and Analysis permanent plots representing 17 different habitat types. Samples of the fungus associated with Armillaria root disease were collected from 23 trees and identified using DNA sequencing. All samples were determined to consist of a single species, Armillaria solidipes Peck [= A. ostoyae (Romagnesi) Herink]. Only 10 of the 76 plots and 5 of the 17 habitat types sampled had Armillaria solidipes present on one or more trees. A. solidipes was more commonly found in mixed-conifer and subalpine forests and was rare in ponderosa pine (Pinus ponderosa Doug. Ex. Larson & C. Larson) forests, which was consistent with previous root disease studies conducted in the Southwest. However, our estimates of Armillaria presence may be conservative since we did not examine entire root systems.