Zip Code 21791 — Union Bridge, MD
21791 is a ZIP Code associated with Union Bridge, MD, located within Frederick. 21791 ranks #16 out of 27 ZIP codes in Frederick County by population (and #234 out of 477 in MD). The area supports an estimated population of 5,340 residents across Data Pending housing units, with a population density of 44.8 people per square mile.
WorldPlaceData database updated: October 2026
📍 View location on OpenStreetMap (39.542670, -77.187130)
| Data Metric | Local Statistic |
|---|
| Postal / Zip Code | 21791 |
| Primary City | Union Bridge |
| State / Province | MD |
| County | Frederick |
| Total Population | 5,340 |
| Median Household Income | Data Pending |
| Total Housing Units | Data Pending |
| Population Density | 44.8 people/sq mi |
| Timezone | America/New_York |
How 21791 Compares
| Metric | ZIP 21791 | Frederick County | MD State Average |
|---|
| Population | 5,340 | 300,100 (Total) | 6,205,597 (Total) |
| Average ZIP Income | Data Pending | N/A | N/A |
| Population Density | 44.8 /sq mi | -- | -- |
| County Pop Rank | #16 of 27 | -- | -- |
Nearby ZIP Codes
Data Sources & Methodology: Geographic coordinates and ZIP Code assignments are derived from underlying geographic and postal datasets. Note that ZIP Codes are USPS postal delivery areas, while Census ZCTAs are statistical approximation areas. Read full methodology →