Joppa is a former colonial town and current planning region of Harford County, Maryland, United States. Joppa was founded as a British settlement on the Gunpowder River in 1707 and designated as the third county seat of Baltimore County in 1712. The original boundaries of Baltimore County were defined in 1659 and contained all of modern day Baltimore County, Baltimore City, Harford and Cecil counties and parts of Howard, Carroll, Anne Arundel and Kent counties. The settlement was named for the Biblical town of Jaffa in the ancient Holy Land of modern day Israel. Joppa's harbor began to silt in due to clearcutting and farming upriver and coupled with multiple outbreaks of diseases such as smallpox and malaria, the county seat was moved to the growing, deep water port of Baltimore in 1768. Joppa's population would decline rapidly thereafter and businesses left for more prosperous environments in the new Baltimore Town.
The town of Joppa near the Western Shore of the Chesapeake Bay was designated as a "Port of Entry" by the colonial legislature, the Maryland General Assembly. It traded internationally in agricultural products, primarily tobacco; the chief commodity crop and currency throughout much of its colonial era.
At its peak, the port was home to about 50 or more homes, the courthouse, two prisons, a church, several inns, shops, and warehouses.
In 1768, the Maryland General Assembly moved the county seat of Baltimore County from Joppa to Baltimore Town, which was developing as a major port.