Jefferson County
Wisconsin · County seat: Jefferson · Active county or equivalent
FIPS code 55055 is Jefferson County, Wisconsin. With a population of 85,932 (2022 ACS estimate), it ranks #20 in Wisconsin and #673 nationally. Jefferson County is part of the Watertown-Fort Atkinson, WI. The state FIPS code for Wisconsin is 55. This code is used in Census Bureau, BLS, EPA, HUD, and USDA federal datasets to identify this county.
County FIPS
55055
Population
85,932
2022 ACS · #673 nationally
Density
154.4/mi²
people per sq mile
Land Area
556
sq miles
Urban/Rural
Nonmetro — urban 20K+, adjacent to metro
RUCC 4
How This FIPS Code Works
The 5-digit FIPS code 55055 is formed by combining the 2-digit state identifier 55 (Wisconsin) with the 3-digit county identifier 055. Together they uniquely identify Jefferson County in every US federal dataset. No two counties share the same 5-digit FIPS code.
Census ACS Data for FIPS 55055
From the 2022 ACS 5-year estimates — the same values you'd retrieve by querying the Census API with county FIPS 55055.
Median Household Income
$77,018
ACS B19013_001E
Poverty Rate
7.6%
ACS B17001 (below poverty level)
Median Age
41.5
ACS B01002_001E
Metropolitan Area
Adjacent Counties (5)
Counties that share a border with Jefferson County. Useful for regional analysis — these are the geographies you'd typically include when studying labor markets, commuting zones, or environmental spillovers around FIPS 55055.
Federal Datasets Using Code 55055
FIPS code 55055 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 55055 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:055",
"in": "state:55",
"key": "YOUR_CENSUS_API_KEY",
}
r = requests.get(url, params=params)
data = r.json() # [[header...], [Jefferson County, Wisconsin, income, pop, ...]-- 5-digit combined FIPS (state + county)
SELECT * FROM your_table WHERE county_fips = '55055';
-- Some datasets store state and county separately
SELECT * FROM your_table
WHERE state_fips = '55'
AND county_fips = '055';
-- ⚠ Never cast to integer — leading zeros are lost:
-- county_fips = 55055 is WRONG for this countylibrary(tidycensus)
get_acs(
geography = "county",
variables = c(income = "B19013_001E", pop = "B01003_001E"),
state = "55",
county = "055",
year = 2022
)ZIP Codes in Jefferson 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 Jefferson County. Why FIPS ≠ ZIP →
| ZIP Code | % in county |
|---|---|
| 53137 | 100.0% |
| 53038 | 100.0% |
| 53551 | 100.0% |
| 53094 | 100.0% |
| 53549 | 100.0% |
| 53156 | 100.0% |
| 53178 | 100.0% |
| 53538 | 98.3% |
| 53036 | 70.5% |
| 53594 | 52.2% |
| 53523 | 34.7% |
| 53190 | 23.8% |
| 53066 | 17.0% |
| 53118 | 12.9% |
| 53534 | 4.9% |
| 53119 | 2.2% |
| 53563 | 1.5% |
| 53559 | 0.7% |
| 53098 | 0.0% |