County outline
Where Monroe County is located
Area breakdown
Land accounts for 18.6% of Monroe County’s measured area and water for 81.4%. Its combined area converts to 13,699.9 square kilometers or approximately 3,385,322 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 983.043 | 2,546.07 | 629,147.5 |
| Water | 4,306.522 | 11,153.841 | 2,756,174.1 |
| Total | 5,289.565 | 13,699.91 | 3,385,321.6 |
How Monroe County compares
By original Census land area, Monroe County ranks #17 of 67 in Florida and #700 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.411 times the Florida county-equivalent median of 696.5 square miles. It accounts for 1.8% of the combined county land area in the state.
See the complete Florida ranking · What counts as a county equivalent?
Population and density of Monroe County
The Census Bureau estimates that 80,406 people lived in Monroe County on July 1, 2025. That ranks #739 of 3,222 county equivalents nationally and #39 of 67 in Florida. Since the April 1, 2020 estimates base of 82,871, the population has declined by 2,465 (−3%), compared with +8.9% for Florida as a whole.
With 983 square miles of land, that is 82 people per square mile (32 per km²), placing Monroe County #1,138 nationally for density and #43 in Florida. The median county equivalent has 47 people per square mile; the Florida median is 209. Put another way, there are about 7.8 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 82,851 | 82,261 | 82,696 | 82,695 | 82,015 | 80,406 |
| Change | — | −590 | +435 | −1 | −680 | −1,609 |
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 Monroe County
5 incorporated places lie at least partly in Monroe County. Together they are home to 42,964 people (53.4%); the other 37,442 (46.6%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Key West city, with 24,999 residents in the county. By land, Marathon city is the largest at 8.447 mi². Among places with at least 1,000 residents in 2020, Marathon city grew fastest since then (+3.3%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Key West cityCounty seat | 24,999 | −5.4% | 5.599 |
| Marathon city | 10,060 | +3.3% | 8.447 |
| Islamorada, Village of Islands village | 6,955 | −2.4% | 6.452 |
| Key Colony Beach city | 741 | −6% | 0.44 |
| Layton city | 209 | −3.2% | 0.162 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Monroe County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Monroe County is a central county of the Key West-Key Largo, FL Micropolitan Statistical Area. Monroe County is the area’s only county equivalent, so the micro area has the same 983 square miles of land. By combined land it ranks #185 of 542 micropolitan areas, and #74 by population. It belongs to the Miami-Port St. Lucie-Fort Lauderdale, FL Combined Statistical Area.
ZIP codes
11 ZIP Code Tabulation Areas have land in Monroe County; 9 of them have most of their land inside the county, and the others mainly cover neighboring areas.
3300133034330363303733040330423304333050330513307034141
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 Monroe County
Monroe County shares a land border with 2 county equivalents. Each of them has more land than Monroe County. The largest neighbor is Collier County (1,997 mi²) and the smallest is Miami-Dade County (1,900 mi²). Together with its neighbors, Monroe County forms a block of 4,880.1 mi² of land, of which it holds 20.1%.
| Bordering county equivalent | Land mi² | Size vs. Monroe | Compare |
|---|---|---|---|
| Collier County | 1,997 | 2× larger | Compare |
| Miami-Dade County | 1,900 | 1.9× larger | Compare |
How big is Monroe County compared with U.S. states?
Monroe County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.1 times as much. Florida’s county land could hold about 55 areas the size of Monroe County.
Another way to picture it: the same land area would fill a square about 31.4 miles (50.5 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 Monroe County?
Monroe County has more land than 2,522 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 Monroe County at #77 nationally by total area, 623 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 81.4%, compared with a national county-equivalent median of 1.2% — 80.2 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 Monroe County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #699 | Concho County, Texas | 983.8 | Compare |
| #700 | Monroe County, Florida | 983 | This county |
| #701 | Bosque County, Texas | 983 | 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 25.586120, -81.022603. 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: 2,546,069,740 m²; AWATER: 11,153,840,985 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 Monroe County?
Monroe County, Florida has 983 square miles (2,546.1 km²) of land and 4,306.5 square miles of water, for a total area of 5,289.6 square miles. It ranks #700 of 3,222 U.S. county equivalents by land area.
Is Monroe County the largest county in Florida?
No. Monroe County ranks #17 of 67 in Florida by land area. The largest is Collier County, with 1,997 square miles of land.
What counties border Monroe County?
Monroe County shares a land border with Miami-Dade County and Collier County.
What is the population of Monroe County?
The Census Bureau estimates Monroe County had 80,406 residents on July 1, 2025, ranking #739 of 3,222 county equivalents. That is 82 people per square mile of land.
What is the county seat of Monroe County?
The county seat of Monroe County is Key West.
What cities and towns are in Monroe County?
Monroe County has 5 incorporated places. The most populous are Key West city, Marathon city, Islamorada, Village of Islands village, Key Colony Beach city, and Layton city; 37,442 residents live outside any incorporated place.
Is Monroe County part of a metropolitan area?
Yes. It is a central county of the Key West-Key Largo, FL Micropolitan Statistical Area.
How many ZIP codes are in Monroe County?
11 ZIP Code Tabulation Areas have land in Monroe County, and 9 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Monroe County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.1 times as much land.
How many acres of land are in Monroe County?
The land measurement converts to approximately 629,148 acres. Including water, total area is approximately 3,385,322 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.