Mercer

Mercer is a county inside New Jersey (FIPS code 34021) that contains 22 USPS ZIP codes covering a combined population of 390,132 according to Census ACS 5-Year Estimates. Counties are the natural bridge between state-level summaries and ZIP-level detail — crime statistics, HUD Fair Market Rents, and childcare pricing are all published at the county level, while household income and housing values are published at the ZIP level. This page reconciles the two views so you can see which ZIPs drive the county totals.

The 22 ZIPs listed below are ordered by population and each links to the full ZIP detail page with Census demographics, housing, income, home-price history, and cross-agency inputs. The most populated ZIP in Mercer is 08540 covering Princeton with 47,115 residents at 350 people per square mile. Population density across ZIPs in this county varies — use the density column to spot urban cores versus rural delivery areas. A single county can contain both a dense downtown ZIP and a large rural ZIP covering several hundred square miles.

Because Mercer uses FIPS code 34021, it joins cleanly to county-level federal datasets: HUD Fair Market Rent tables, FBI Uniform Crime Report data, and the Department of Labor National Database of Childcare Prices all key off the same code. That is how neighborhood scorecards combine ZIP-level Census demographics with county-level safety and affordability metrics. All data on this page comes from U.S. Census Bureau ACS 2023 5-Year Estimates and USPS ZIP Code Tabulation Area files — no estimates, no proprietary sources, no editorial scoring.