Millbourne Borough is a self-governing municipal borough in Delaware County, Pennsylvania, United States. As of the 2020 census, the population is 1,212. Millbourne borders Philadelphia along Cobbs Creek. The name "Millbourne" comes from the word Mill and "bourne" meaning creek. Millbourne was settled by Samuel Sellers in 1682. Samuel's descendants later owned a gristmill in Millbourne called Millbourne Mills. In the early 1900s, developers Samuel Shoemaker and John L. Fry developed housing in Millbourne, leading to its separation from Upper Darby and its official incorporation as a borough in 1909.