Grantsville is located in Garrett County
30 miles west of Cumberland
on I-Alt 40 on the banks of the Casselman River near Casselman River Bridge State Park
. Grantsville took its name from Daniel Grant, a Baltimorean who is said to have helped settle the area during the 1790s. The Casselman Hotel, Little Crossings Inn, now the Penn Alps, and Staton's Mill, all founded 1797-1824, are among the buildings that remain from that era; all are still in use.
About a half mile east of town, US 40 crosses the Casselman Bridge, an 80-foot stone span built in 1813 for the National Road. At the time of its construction it was the country's longest single-span stone arch bridge. Nearby Casselman River Bridge State Park has picnic facilities.