The Calapooya Mountains are a short mountain range in southwestern Oregon in the United States. The range runs for approximately 60 mi (100 km) west from the Cascade Range between Eugene (N) and Roseburg (S). The range separates the basins of the Willamette River to the north with that of the Umpqua River to the south. The highest peaks in the range include Scott Mountain (elevation 4250 ft/1296 m) approximatley 20 mi (32 km) northeast of Roseburg. The North Umpqua River flows along the southern edge of the range. The crest of the range is sometimes called the Calapooya Divide.

The mountains have been an important timber source in the 20th century. The eastern end of the mountains are largely within the Umpqua National Forest and Willamette National Forest.

Throughout the history of the region the range has provided a geographic and cultural barrier between the Willamette Valley and the South Umpqua Valley, effectively separating Western Oregon from Southern Oregon. In the 19th century, it separated the tribal domains of the Kalapuya and Coquille tribes of Native Americans, both of which ceded their lands to the U.S. government in the 1854 Kalapuya Treaty. During the 1840s the mountains became an inconvenient barrier for white settlers seeking to move into southern Oregon or to move southward to the California gold fields. The Applegate Trail, blazed in the late 1840s provided the first reliable path for white settlement through the western end of the mountains. Interstate 5 essentially follows the route of the rail between Eugene and Roseburg.