Mount Joy is a borough in Lancaster County, Pennsylvania, United States. The population was 7,410 at the 2010 census, and an estimated 8,278 in 2019.
The name is often shortened to "Mt Joy", as in Mencken (1963). However, citizens of the town often point out that this abbreviation is not proper because the town is not named for a mountain but is named after the "Good Ship" Mountjoy which famously broke a Catholic siege during the Siege of Derry. Due to the early settlement of the Protestant Scots-Irish in this region of Pennsylvania, many of the municipalities in the area were given names common to the North of Ireland, such as Derry Township, Londonderry Township, South Londonderry Township, Mount Joy Township, East Donegal Township, West Donegal Township, and Rapho Township.
Mount Joy is often named in lists of "delightfully-named towns" in Pennsylvania Dutch Country, along with Intercourse, Blue Ball, Lititz, Bareville, Bird-in-Hand and Paradise.
Mount Joy is located in northwestern Lancaster County at 40°6′36″N 76°30′40″W (40.109895, -76.510977). Pennsylvania Route 230 passes through the center of town as Main Street, leading southeast 12 miles (19 km) to Lancaster, the county seat, and northwest 6 miles (10 km) to Elizabethtown. Harrisburg, the state capital, is 25 miles (40 km) to the northwest via PA-230. PA-772 crosses PA-230 west of the borough center and leads northeast 7 miles (11 km) to Manheim and southwest 5 miles (8 km) to Marietta on the Susquehanna River.
According to the United States Census Bureau, the borough has a total area of 2.4 square miles (6.3 km2), of which 0.02 square miles (0.04 km2), or 0.64%, are water. Little Chiques Creek, a south-flowing tributary of Chiques Creek and part of the Susquehanna River watershed, crosses the eastern side of the borough.