Dendroctonus pseudotsugae Hopkins infests Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, throughout the distribution of that tree species from British Columbia to northern Mexico. The subspecies Dendroctonus pseudotsugae barragani Furniss was described from the mountains of Chihuahua, Sierra Madre Occidental, Mexico, whereas the nominal subspecies, Dendroctonus pseudotsugae pseudotsugae Hopkins, occurs north of Mexico. The description of D. p. barragani was based on the only known Mexican population at that time. More recently, new populations of this beetle have been discovered at 13 additional localities in Chihuahua, Durango, Coahuila, and Nuevo Leon, Mexico. To test whether these additional populations support the existence of two subspecies, we performed a taxonomic reassessment combining molecular markers (cytochrome oxidase I), morphological characters used in the original description, and newly described morphological characters. Phylogenetic analysis of 89 haplotypes confirms that the Mexican populations are distinct from the sampled populations in the United States and Canada. Morphological analysis indicates that intraspecific variation is greater than previously considered within Mexican populations. However, at least seven characters on the head, pronotum, and elytra (including three previously undescribed characters of frons sculpture) consistently discriminate among Canada—U.S. and Mexico populations. The extension of the known distribution of this beetle in Mexico and verification of its subspecific status will aid in the management and conservation of Pseudotsuga in Mexico.