Rose Valley is a small, historic borough in Delaware County, Pennsylvania, United States. Its area is 0.73 square miles (1.9 km2), and the population was 913 at the 2010 census. The area was settled by Quaker farmers in 1682, and later water mills along Ridley Creek drove manufacturing in the nineteenth century.

Delaware County, colloquially referred to as Delco, is a county in the Commonwealth of Pennsylvania. With a population of 576,830 as of the 2020 census, it is the fifth-most populous county in Pennsylvania and the third-smallest in area. The county was created on September 26, 1789, from part of Chester County and named for the Delaware River. The county is part of the Southeast Pennsylvania region of the state.