County outline
Where St. Lucie County is located
Area breakdown
Land accounts for 83.1% of St. Lucie County’s measured area and water for 16.9%. Its combined area converts to 1,781.9 square kilometers or approximately 440,320 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 571.856 | 1,481.1 | 365,987.8 |
| Water | 116.144 | 300.812 | 74,332.2 |
| Total | 688 | 1,781.912 | 440,320 |
How St. Lucie County compares
By original Census land area, St. Lucie County ranks #49 of 67 in Florida and #1755 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.821 times the Florida county-equivalent median of 696.5 square miles. It accounts for 1.1% of the combined county land area in the state.
See the complete Florida ranking · What counts as a county equivalent?
Population and density of St. Lucie County
The Census Bureau estimates that 402,449 people lived in St. Lucie County on July 1, 2025. That ranks #189 of 3,222 county equivalents nationally and #20 of 67 in Florida. Since the April 1, 2020 estimates base of 329,226, the population has grown by 73,223 (+22.2%), compared with +8.9% for Florida as a whole.
With 571.9 square miles of land, that is 704 people per square mile (272 per km²), placing St. Lucie County #258 nationally for density and #12 in Florida. The median county equivalent has 47 people per square mile; the Florida median is 209. Put another way, there are about 0.909 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 331,453 | 344,403 | 360,720 | 377,820 | 391,592 | 402,449 |
| Change | — | +12,950 | +16,317 | +17,100 | +13,772 | +10,857 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in St. Lucie County
3 incorporated places lie at least partly in St. Lucie County. Together they are home to 320,441 people (79.6%); the other 82,008 (20.4%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Port St. Lucie city, with 268,062 residents in the county. The county seat, Fort Pierce city, has 51,737 residents. Among places with at least 1,000 residents in 2020, Port St. Lucie city grew fastest since then (+30.9%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Port St. Lucie city | 268,062 | +30.9% | 119.2 |
| Fort Pierce cityCounty seat | 51,737 | +9% | 24.9 |
| St. Lucie Village town | 642 | +1.7% | 0.905 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside St. Lucie County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
St. Lucie County is a central county of the Port St. Lucie, FL Metropolitan Statistical Area. Its 2 county equivalents have 568,721 residents on 1,115.7 square miles of land; St. Lucie County accounts for 51.3% of the land and 70.8% of the residents. By combined land it ranks #268 of 393 metropolitan areas, and #105 by population. It belongs to the Miami-Port St. Lucie-Fort Lauderdale, FL Combined Statistical Area.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| St. Lucie County | 402,449 | 571.9 |
| Martin County | 166,272 | 543.9 |
ZIP codes
17 ZIP Code Tabulation Areas have land in St. Lucie County; 14 of them have most of their land inside the county, and the others mainly cover neighboring areas.
3494534946349473494934950349513495234953349573497234981349823498334984349863498734990
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering St. Lucie County
St. Lucie County shares a land border with 3 county equivalents. It has more land than 2 of them. The largest neighbor is Okeechobee County (769.3 mi²) and the smallest is Indian River County (502.6 mi²). Together with its neighbors, St. Lucie County forms a block of 2,387.6 mi² of land, of which it holds 24%.
| Bordering county equivalent | Land mi² | Size vs. St. Lucie | Compare |
|---|---|---|---|
| Okeechobee County | 769.3 | 1.3× larger | Compare |
| Martin County | 543.9 | 1.1× smaller | Compare |
| Indian River County | 502.6 | 1.1× smaller | Compare |
How big is St. Lucie County compared with U.S. states?
St. Lucie County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.8 times as much. Florida’s county land could hold about 94 areas the size of St. Lucie County.
Another way to picture it: the same land area would fill a square about 23.9 miles (38.5 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about St. Lucie County?
St. Lucie County has more land than 1,467 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places St. Lucie County at #1,470 nationally by total area, 285 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.
Its water share is 16.9%, compared with a national county-equivalent median of 1.2% — 15.7 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside St. Lucie County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1754 | Alpena County, Michigan | 571.9 | Compare |
| #1755 | St. Lucie County, Florida | 571.9 | This county |
| #1756 | Franklin County, Kansas | 571.8 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 27.379814, -80.443536. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,481,099,209 m²; AWATER: 300,812,756 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is St. Lucie County?
St. Lucie County, Florida has 571.9 square miles (1,481.1 km²) of land and 116.1 square miles of water, for a total area of 688 square miles. It ranks #1755 of 3,222 U.S. county equivalents by land area.
Is St. Lucie County the largest county in Florida?
No. St. Lucie County ranks #49 of 67 in Florida by land area. The largest is Collier County, with 1,997 square miles of land.
What counties border St. Lucie County?
St. Lucie County shares a land border with Martin County, Okeechobee County, and Indian River County.
What is the population of St. Lucie County?
The Census Bureau estimates St. Lucie County had 402,449 residents on July 1, 2025, ranking #189 of 3,222 county equivalents. That is 704 people per square mile of land.
What is the county seat of St. Lucie County?
The county seat of St. Lucie County is Fort Pierce.
What cities and towns are in St. Lucie County?
St. Lucie County has 3 incorporated places. The most populous are Port St. Lucie city, Fort Pierce city, and St. Lucie Village town; 82,008 residents live outside any incorporated place.
Is St. Lucie County part of a metropolitan area?
Yes. It is a central county of the Port St. Lucie, FL Metropolitan Statistical Area, which has 2 county equivalents and 568,721 residents.
How many ZIP codes are in St. Lucie County?
17 ZIP Code Tabulation Areas have land in St. Lucie County, and 14 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does St. Lucie County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.8 times as much land.
How many acres of land are in St. Lucie County?
The land measurement converts to approximately 365,988 acres. Including water, total area is approximately 440,320 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.