Garrett County is the westernmost county of the U.S. state of Maryland. Created from Allegany County, Maryland in 1872 it was the last Maryland county to be formed. It was named for John Work Garrett (1820–1884). The county has long been part of the media market of Pittsburgh, Pennsylvania.
The Commonwealth of Pennsylvania is to the north. The Maryland–Pennsylvania boundary was surveyed and marked between April 1765 and October 1767 by astronomer Charles Mason and surveyor Jeremiah Dixon. This boundary is commonly known as the Mason-Dixon Line. The eastern border with Allegany County was defined by the Bauer Report, submitted to Governor Lloyd Lowndes, Jr. on November 9, 1898. The Potomac River and State of West Virginia lie to the south and west.
Garrett County lies in the Allegheny Mountains, which here form the western flank of the Appalachian Mountain Range. Hoye-Crest, a summit along Backbone Mountain, is the highest point in Maryland.
The Eastern Continental Divide runs along portions of Backbone Mountain. The western part of the county, drained by the Youghiogheny River, is the only part of Maryland within the Mississippi River drainage basin. All other parts of the county are in the Chesapeake Bay basin.
Garrett County contains over 76,000 acres (310 km2) of parks, lakes, and publicly accessible forestland. Popular activities in the county include camping, hiking, backpacking, rock climbing, alpine and cross county skiing, snowmobiling, hunting, ice fishing, fly fishing, whitewater canoeing, kayaking, rafting, boating, swimming, sailing, horseback riding, and water skiing.
The National Register of Historic Places listings in Garrett County, Maryland has 20 National Register of Historic Places properties and districts, including Casselman Bridge, National Road a National Historic Landmark. Garrett County is part of Maryland's 6th congressional district and Oakland is the county seat.