St. Croix County
Wisconsin · County seat: Hudson · Active county or equivalent
FIPS code 55109 is St. Croix County, Wisconsin. With a population of 93,752 (2022 ACS estimate), it ranks #17 in Wisconsin and #637 nationally. St. Croix County is part of the Minneapolis-St. Paul-Bloomington, MN-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
55109
Population
93,752
2022 ACS · #637 nationally
Density
129.8/mi²
people per sq mile
Land Area
722
sq miles
Urban/Rural
Metro — 1M+ population
RUCC 1
How This FIPS Code Works
The 5-digit FIPS code 55109 is formed by combining the 2-digit state identifier 55 (Wisconsin) with the 3-digit county identifier 109. Together they uniquely identify St. Croix County in every US federal dataset. No two counties share the same 5-digit FIPS code.
Census ACS Data for FIPS 55109
From the 2022 ACS 5-year estimates — the same values you'd retrieve by querying the Census API with county FIPS 55109.
Median Household Income
$97,950
ACS B19013_001E
Poverty Rate
5.9%
ACS B17001 (below poverty level)
Median Age
39.7
ACS B01002_001E
Metropolitan Area
Adjacent Counties (5)
Counties that share a border with St. Croix County. Useful for regional analysis — these are the geographies you'd typically include when studying labor markets, commuting zones, or environmental spillovers around FIPS 55109.
Federal Datasets Using Code 55109
FIPS code 55109 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 55109 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:109",
"in": "state:55",
"key": "YOUR_CENSUS_API_KEY",
}
r = requests.get(url, params=params)
data = r.json() # [[header...], [St. Croix County, Wisconsin, income, pop, ...]-- 5-digit combined FIPS (state + county)
SELECT * FROM your_table WHERE county_fips = '55109';
-- Some datasets store state and county separately
SELECT * FROM your_table
WHERE state_fips = '55'
AND county_fips = '109';
-- ⚠ Never cast to integer — leading zeros are lost:
-- county_fips = 55109 is WRONG for this countylibrary(tidycensus)
get_acs(
geography = "county",
variables = c(income = "B19013_001E", pop = "B01003_001E"),
state = "55",
county = "109",
year = 2022
)ZIP Codes in St. Croix 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 St. Croix County. Why FIPS ≠ ZIP →
| ZIP Code | % in county |
|---|---|
| 54023 | 100.0% |
| 54082 | 100.0% |
| 54028 | 100.0% |
| 54027 | 100.0% |
| 54015 | 100.0% |
| 54016 | 100.0% |
| 54025 | 100.0% |
| 54002 | 96.9% |
| 54017 | 96.8% |
| 54013 | 96.5% |
| 54007 | 78.4% |
| 54022 | 38.8% |
| 54026 | 24.3% |
| 54005 | 19.7% |
| 54749 | 16.1% |
| 54767 | 12.1% |
| 54734 | 6.0% |
| 54020 | 1.0% |