Ridley Township was first settled in 1643 by the Swedes in what is now Tinicum Township. The name Ridley was first used in 1687 named by John Simcock, a large landowner for his village in Cheshire, England. Tinicum township left Ridley in 1790, and for the next 80 years, it was mostly farmland with some mills and quarry operations. The population in 1870 was just over 1100 people. A new railroad line, the Darby improvement came through in 1872, establishing the towns of Eddystone, Ridley Park, Prospect Park, Norwood, Glenolden, and Rutledge. All of these towns left Ridley Township between 1887 and 1894.

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Ridley Township encompasses the following towns and communities, which are all part of the township, and are known by locals as Ridley, as they share the same taxes, school district, library, police department located in Folsom: Crum Lynne, Folsom, Holmes, Leedom, Milmont Park, Secane, Swarthmorewood, and Woodlyn.

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Ridley Township is in southeastern Delaware County, northeast of Chester and southeast of Media, the county seat. The borough of Rutledge is in the northern part of the township but is a separate municipality. The unincorporated communities of Folsom and Woodlyn occupy the central and western parts of the township, respectively.