Joppa is a former town and current planning region of Harford County, Maryland. Joppa was founded as a British colonial settlement in the early 18th century, and takes its name from the biblical town of Joppa (Jaffa, Israel). In 1962, Joppatowne, one of the first of a new generation of planned unit developments (PUD) in the United States, was launched by the Panitz Company. McComas Institute was listed on the National Register of Historic Places in 1980. Olney was listed in 1987 and Whitaker's Mill Historic District in 1990.