Montgomery County
Pennsylvania · County seat: Norristown · Active county or equivalent
FIPS code 42091 is Montgomery County, Pennsylvania. With a population of 856,399 (2022 ACS estimate), it ranks #3 in Pennsylvania and #68 nationally. Montgomery County is part of the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD. The state FIPS code for Pennsylvania is 42. This code is used in Census Bureau, BLS, EPA, HUD, and USDA federal datasets to identify this county.
County FIPS
42091
Population
856,399
2022 ACS · #68 nationally
Density
1,772.9/mi²
people per sq mile
Land Area
483
sq miles
Urban/Rural
Metro — 1M+ population
RUCC 1
How This FIPS Code Works
The 5-digit FIPS code 42091 is formed by combining the 2-digit state identifier 42 (Pennsylvania) with the 3-digit county identifier 091. Together they uniquely identify Montgomery County in every US federal dataset. No two counties share the same 5-digit FIPS code.
Census ACS Data for FIPS 42091
From the 2022 ACS 5-year estimates — the same values you'd retrieve by querying the Census API with county FIPS 42091.
Median Household Income
$107,441
ACS B19013_001E
Poverty Rate
6.3%
ACS B17001 (below poverty level)
Median Age
41.2
ACS B01002_001E
Metropolitan Area
Adjacent Counties (6)
Counties that share a border with Montgomery County. Useful for regional analysis — these are the geographies you'd typically include when studying labor markets, commuting zones, or environmental spillovers around FIPS 42091.
Federal Datasets Using Code 42091
FIPS code 42091 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 42091 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:091",
"in": "state:42",
"key": "YOUR_CENSUS_API_KEY",
}
r = requests.get(url, params=params)
data = r.json() # [[header...], [Montgomery County, Pennsylvania, income, pop, ...]-- 5-digit combined FIPS (state + county)
SELECT * FROM your_table WHERE county_fips = '42091';
-- Some datasets store state and county separately
SELECT * FROM your_table
WHERE state_fips = '42'
AND county_fips = '091';
-- ⚠ Never cast to integer — leading zeros are lost:
-- county_fips = 42091 is WRONG for this countylibrary(tidycensus)
get_acs(
geography = "county",
variables = c(income = "B19013_001E", pop = "B01003_001E"),
state = "42",
county = "091",
year = 2022
)ZIP Codes in Montgomery 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 Montgomery County. Why FIPS ≠ ZIP →
| ZIP Code | % in county |
|---|---|
| 19453 | 100.0% |
| 19072 | 100.0% |
| 19075 | 100.0% |
| 19090 | 100.0% |
| 19095 | 100.0% |
| 19401 | 100.0% |
| 19403 | 100.0% |
| 19405 | 100.0% |
| 19406 | 100.0% |
| 19422 | 100.0% |
| 19426 | 100.0% |
| 19428 | 100.0% |
| 19435 | 100.0% |
| 19436 | 100.0% |
| 19437 | 100.0% |
| 19438 | 100.0% |
| 19444 | 100.0% |
| 19446 | 100.0% |
| 19456 | 100.0% |
| 19462 | 100.0% |
| 19468 | 100.0% |
| 19472 | 100.0% |
| 19473 | 100.0% |
| 19474 | 100.0% |
| 19477 | 100.0% |
| 19490 | 100.0% |
| 19492 | 100.0% |
| 18074 | 100.0% |
| 18076 | 100.0% |
| 18915 | 100.0% |
Showing top 30 of 71 ZIP codes by residential address share.