COUNTY · NJ
Mercer County, New Jersey
Mercer County is a county in New Jersey with FIPS code 34021 and an estimated population of 381,671 (Census 2023), 12th largest of 21 in the state.
County facts
- Name
- Mercer County
- State
- New Jersey
- Type
- county
- FIPS code
- 34021
- State FIPS
- 34
- Population (2023)
- 381,671
- Change since 2020
- -1.2%
- State rank
- 12 of 21
Population is the Census Bureau’s Vintage 2023 estimate.
Other counties in New Jersey
Questions
What is the FIPS code for Mercer County?
Mercer County, New Jersey has the five-digit FIPS code 34021: 34 for the state and 021 for the county.
What state is Mercer County in?
Mercer County is in New Jersey.
How do I know if an address is in this county?
Use the address lookup. ZIP codes and city names can cross county lines, so an address is the reliable check.
Sources: U.S. Census Bureau geographic reference files; Census Bureau Population Estimates, Vintage 2023. Last reviewed 2026-10-27.