Rheems is an unincorporated community and census-designated place (CDP) in Lancaster County, Pennsylvania, United States, between the boroughs of Elizabethtown and Mount Joy. The population was 1,598 during the 2010 census.
Rheems is located in western Lancaster County at 40°07′39″N 76°33′58″W. It is mainly in West Donegal, but with the portion on the north side of Harrisburg Avenue lying in Mount Joy Township. The center of Elizabethtown is 2.5 miles (4.0 km) northwest of Rheems, and the center of Mount Joy is 4 miles (6 km) to the southeast. Lancaster, the county seat, is 16 miles (26 km) southeast of Rheems.
According to the United States Census Bureau, the CDP has a total area of 1.2 square miles (3.1 km2), of which 1.3 acres (5,432 m2), or 0.18%, are water. Rheems is drained by the headwaters of Donegal Creek, which flows south to join Chiques Creek just before entering the Susquehanna River.
At the 2000 census there were 1,557 people, 513 households, and 439 families living in the CDP. The population density was 1,321.7 people per square mile (509.5/km2). There were 521 housing units at an average density of 442.3/sq mi (170.5/km2). The racial makeup of the CDP was 97.75% White, 0.26% African American, 0.13% Native American, 0.45% Asian, 0.13% Pacific Islander, 0.32% from other races, and 0.96% from two or more races.