Mercer County

How This FIPS Code Works

Census ACS Data for FIPS 34021

From the 2022 ACS 5-year estimates — the same values you'd retrieve by querying the Census API with county FIPS 34021.

Metropolitan Area

Adjacent Counties (6)

Counties that share a border with Mercer County. Useful for regional analysis — these are the geographies you'd typically include when studying labor markets, commuting zones, or environmental spillovers around FIPS 34021.

Federal Datasets Using Code 34021

FIPS code 34021 appears as the county identifier in the following federal datasets. Analysts joining data across these sources use this code as the common geographic key.

Using FIPS Code 34021 in Code

Common patterns for querying federal datasets by this county's FIPS code. The leading zeros are significant — always treat FIPS codes as strings, not integers.

import requests

url = "https://api.census.gov/data/2022/acs/acs5"
params = {
    "get":  "NAME,B19013_001E,B01003_001E",
    "for":  "county:021",
    "in":   "state:34",
    "key":  "YOUR_CENSUS_API_KEY",
}
r = requests.get(url, params=params)
data = r.json()  # [[header...], [Mercer County, New Jersey, income, pop, ...]

-- 5-digit combined FIPS (state + county)
SELECT * FROM your_table WHERE county_fips = '34021';

-- Some datasets store state and county separately
SELECT * FROM your_table
WHERE state_fips = '34'
  AND county_fips = '021';

-- ⚠ Never cast to integer — leading zeros are lost:
-- county_fips = 34021 is WRONG for this county

library(tidycensus)

get_acs(
  geography = "county",
  variables = c(income = "B19013_001E", pop = "B01003_001E"),
  state     = "34",
  county    = "021",
  year      = 2022
)

ZIP Codes in Mercer County

ZIP codes do not align perfectly with county boundaries — a single ZIP code can span multiple counties, and a county can contain parts of many ZIP codes. The ratios below (from the Census 2020 ZCTA relationship file) show the land area share of each ZCTA that falls within Mercer County. Why FIPS ≠ ZIP →