The Delaware Valley is a term used widely to refer to the metropolitan area centered on the city of Philadelphia in the United States. The term is derived from the Delaware River, which flows through it. The Office of Management and Budget officially defines the region as the Philadelphia–Camden–Wilmington Metropolitan Statistical Area.
The Delaware Valley is composed of several counties in Delaware, New Jersey, Maryland, and Pennsylvania, and contains a population of 5.83 million (as of the 2006 Census Bureau estimate). Philadelphia, being the region's major commercial, cultural, and industrial center, maintains a rather large sphere of influence that affects those counties that immediately surround it. The majority of the region's populace resides in Pennsylvania and New Jersey.
The Philadelphia–Camden–Wilmington Metropolitan Statistical Area is the fifth-largest metropolitan area in the United States and is located towards the southern end of the BosWash megalopolis, the name given for a group of metropolitan areas in the northeastern United States, extending from Boston to Washington, D.C.
Based on commuter flows, the OMB also defines a wider labor market region known as the Philadelphia–Camden–Vineland Combined Statistical Area (CSA). This wider region adds the metropolitan areas of Vineland and Reading and has a total population of 6.38 million.
Additionally, the counties of Lancaster, Lehigh, and Northampton, all in Pennsylvania, and Mercer, in New Jersey, are within the Philadelphia media zone. Philadelphia ranks #4, behind only New York, Los Angeles, and Chicago, in Nielsen Media Market size rankings.
