Garrett County is located in the extreme western section of Maryland. It is bordered on the north by Pennsylvania and on the west and south by West Virginia. Roughly triangular in shape and containing 662 square miles, it is the second largest county of Maryland in land area. The Potomac River forms the southern boundary and meanders irregularly northeastward to the Allegany County line. The 1990 population is approximately 40 persons per square mile. It is among the more sparsely populated counties in the state of Maryland.
The topography of Garrett County is largely mountains. All of the county lies within the Appalachian Plateau. The average elevation of the county is 2,300 feet above sea level. There are five main mountain ridges: Backbone Mountain, Negro Mountain, Savage Mountain, Meadow Mountain, and Winding Ridge. The highest point in the county is Backbone Mountain, 3,360 feet. The lowest point, 900 feet, is in the middle of Savage River where it empties into the Potomac.
There is a continental divide in Garrett County. It runs along the crest of Backbone and Meadow Mountains; the water flowing down the east slope goes into the Chesapeake Bay via the Potomac River. The water on the west slope flows into the Gulf of Mexico, via the Youghiogheny, Monongahela, Ohio, and Mississippi Rivers. The main tributary of the Potomac is the Savage River on which a large flood control dam was built. The Casselman River is the main tributary of the Youghiogheny.