Fallston is a census-designated place (CDP) in Harford County, Maryland, United States. The population was 8,427 at the 2000 census. It is a semi-rural community consisting mostly of farms and suburban-like developments and is a good example of an "exurb". Until 1958, this community was served by the Maryland and Pennsylvania Railroad at milepost 22.3.
Fallston is located at 39°31′55″N 76°26′17″W / 39.53194°N 76.43806°W / 39.53194; -76.43806 (39.532006, -76.438021).
According to the United States Census Bureau, the CDP has a total area of 14.0 square miles (36.3 km²), all of it land.