'Mercer County, NJ' definitions:

Mercer -- U.S. County in New Jersey

From: Gazetteer 2000
Name :
Mercer -- U.S. County in New Jersey
Population (2000) :
350761
Housing Units (2000) :
133280
Land area (2000) :
225.929010 sq. miles (585.153425 sq. km)
Water area (2000) :
2.906802 sq. miles (7.528582 sq. km)
Total area (2000) :
228.835812 sq. miles (592.682007 sq. km)
Located within :
New Jersey (NJ), FIPS 34
Location :
40.252908 N, 74.711654 W