Residential delivery area · Maryland
ZIP Code 20634: California (Great Mills), MD
ZIP code 20634 is in California (postal name Great Mills), Maryland, entirely in St. Mary's County (Census 2020 ZIP-county file). About 7,100 people live there (Census Bureau, ACS 2020-2024). Median household income is $139,375 (Census Bureau, ACS 2020-2024). By Census place, 51% of its land lies in California (a census-designated place), and 3% in smaller places; 45% is outside any Census place.
- ACS2020-24
- Census2020
- FHFA2025
- ZBP2023
- IRS2022
- Town
- Great Mills · its only residential ZIP
- County
- St. Mary's County
- Census places
- California census-designated place
- Metro area
- Lexington Park, MD
- House district
- MD-5 119th Congress
- State
- Maryland
- Time zone
- Eastern
- Land area
- 7.0 sq mi · 1,014 people per sq mi
Where is ZIP code 20634?
20634 centers on 38.242°, -76.498° and covers 7.0 square miles of land plus 0.1 of water. It borders 5 ZIP codes: 20620, 20653, 20619, 20692, 20630.
The map draws ZIP code areas only. For the streets inside 20634, open its center on OpenStreetMap.
Source: U.S. Census Bureau, 2020 ZCTA cartographic boundaries and the 2023 Gazetteer (2020 ZCTAs); ZIP-to-county shares, Census places and House districts (119th Congress) from the Census 2020 relationship files (shares of land); metro area from the OMB delineation (July 2023); town name and time zone from simplemaps US ZIP Codes (CC BY 4.0).
How does 20634 compare with the rest of St. Mary's County?
| Measure | 20634 | In St. Mary's County | In MD |
|---|---|---|---|
| People (ACS 2020-2024) | 7,088 | 6th of 27 | 207th of 477 |
| Median household income | $139k | 4th of 8 | 75th of 293 |
| Median home value | $342k | 9th of 9 | 233rd of 320 |
Its median household income is higher than in 95% of U.S. residential ZIP codes, and it is denser than 78% of all U.S. residential ZIP codes. ZIP codes at the ACS caps ($250,000 or more for household income, $2,000,000 or more for home value) share the top rank.
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B01003, B19013, B25077); ranks by PlainZIP over residential ZIP codes (ZCTAs).
How many people live in 20634?
The 2020 Census counted 6,984 people in 20634; the ACS, which samples households over 2020-2024, estimates 7,088. Its boundary changed between the 2010 and 2020 censuses, so the two counts are not compared.
- People, ACS 2020-2024
- 7,088±1,304 (90% margin)
- 2020 Census count
- 6,984
- Households
- 2,694
- Median age
- 32.0
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B01003, B01002, B11001); 2020 Census (DHC P1); 2010 Census (SF1 P1).
Who lives in 20634?
Of the 7,088 people the ACS estimates in 20634, 24.7% are under 18 and 8.4% are 65 or older. The largest group by race and Hispanic origin is White (not Hispanic) (55.2%), then Black (not Hispanic) (27.8%).
- Under 1824.7%
- 18 to 6466.8%
- 65 and older8.4%
- White, not Hispanic55.2%
- Black, not Hispanic27.8%
- Hispanic or Latino8.5%
- Other or two or more5.7%
- Asian, not Hispanic2.8%
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B01001 age by sex, B03002 Hispanic or Latino origin by race); shares of the estimated population, small ZIP codes carry wide margins.
What do households in 20634 earn?
Median household income is $139,375 (ACS 2020-2024), the 4th highest of the 8 ranked ZIP codes in St. Mary's County.
- Median household income
- $139,375±$17,358
- Income per person
- $61,800
- Below the poverty line
- 4.7%
- Unemployed (of the labor force)
- 1.3%
- Adults 25+ with a bachelor's degree
- 40.3%
- Adjusted gross income per tax return, 2022
- $80,9743,560 returns; wages 82% of AGI (IRS)
Source: U.S. Census Bureau, ACS 2020-2024 and 2015-2019 5-year estimates (B19013, B19301, B17001, B23025, B15003; 2015-2019 dollars converted with the BLS CPI-U, 1.22699); IRS Statistics of Income, ZIP code data, tax year 2022 (adjusted gross income per return, filed under the address on the return).
What are homes worth in 20634?
FHFA's house price index for 20634, built from repeat sales and appraisals of the same homes, rose 89% from 2015 to 2025 and rose 57% from 2020 to 2025, and moved +18.9% in 2025.
- Median home value (owners' estimate)
- $342,300
- Median gross rent
- $1,814
- Homes owned by their occupants
- 65.4%
- Housing units
- 3,026
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B25077, B25064, B25003, B25001); FHFA House Price Index, annual five-digit ZIP, updated 2026-03-31.
What businesses are in 20634?
48 business establishments had a location in this ZIP code in 2023, the same count as in 2018; the most are in construction (ZIP Code Business Patterns).
- Construction11
- Retail trade8
- Other services (except public administration)8
- Administrative and support and waste management and remediation services7
- Health care and social assistance6
- Real estate and rental and leasing5
Source: U.S. Census Bureau, ZIP Code Business Patterns 2023 and 2018 (establishments with paid employees, by the business's ZIP code).
Which ZIP codes are next to 20634?
| ZIP | Town | People | Household income | Distance |
|---|---|---|---|---|
| 20620 | Callaway | 1,115 | $166k | 1.4 mi |
| 20653 | Lexington Park | 26,852 | $103k | 3.8 mi |
| 20619 | California | 14,212 | $119k | 3.9 mi |
| 20692 | Valley Lee | 505 | $201k | 4.2 mi |
| 20630 | Drayden | 559 | $233k | 5.9 mi |
| 20667 | Park Hall | 150 | – | 3.3 mi (near) |
| 20686 | Saint Marys City | 971 | – | 5.2 mi (near) |
| 20670 | Patuxent River | 2,046 | $70k | 5.7 mi (near) |
Source: PlainZIP from the Census 2020 ZCTA boundaries (shared edges) and internal points; figures ACS 2020-2024.