County in the New River Valley of Virginia, with its center approximately 4.5 hours southwest of Washington, DC and 3.5 hours WSW of Richmond. Bordered on the west by the New River, with Pulaski County across the river, on the east by Roanoke County, on the south by Floyd County, and the north by Giles County. The independent city of Radford is cut out of the southwest corner of the county, along the New River.

The county is centered on Blacksburg, but the county seat is at Christiansburg. Outside of Blacksburg, with Virginia Tech and all the derivative services and industries that result from it, Montgomery County is fairly poor and uneducated, like many other parts of Appalachia.