County outline
Where Suffolk County is located
Area breakdown
Land accounts for 48.5% of Suffolk County’s measured area and water for 51.5%. Its combined area converts to 311.4 square kilometers or approximately 76,943 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 58.258 | 150.888 | 37,285.1 |
| Water | 61.965 | 160.489 | 39,657.6 |
| Total | 120.223 | 311.376 | 76,942.7 |
How Suffolk County compares
By original Census land area, Suffolk County ranks #13 of 14 in Massachusetts and #3119 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.108 times the Massachusetts county-equivalent median of 540.2 square miles. It accounts for 0.7% of the combined county land area in the state.
See the complete Massachusetts ranking · What counts as a county equivalent?
Population and density of Suffolk County
The Census Bureau estimates that 791,891 people lived in Suffolk County on July 1, 2025. That ranks #85 of 3,222 county equivalents nationally and #4 of 14 in Massachusetts. Since the April 1, 2020 estimates base of 800,934, the population has declined by 9,043 (−1.1%), compared with +1.7% for Massachusetts as a whole.
With 58.3 square miles of land, that is 13,593 people per square mile (5,248 per km²), placing Suffolk County #7 nationally for density and #1 in Massachusetts. The median county equivalent has 47 people per square mile; the Massachusetts median is 673. Put another way, there are about 0.047 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 791,372 | 777,600 | 778,090 | 784,637 | 793,535 | 791,891 |
| Change | — | −13,772 | +490 | +6,547 | +8,898 | −1,644 |
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 Suffolk County
Suffolk County is divided into 4 cities and towns. In Massachusetts, county subdivisions are local governments, and together they cover all of the county’s land and residents.
The most populous is Boston city, with 672,973 residents (85% of the county), and it is also the largest by land at 48.3 mi².
| County subdivision | Population 2025 | Since 2020 | Land mi² | Share of county land |
|---|---|---|---|---|
| Boston cityCounty seat | 672,973 | −0.8% | 48.3 | 83% |
| Revere city | 60,141 | −3.4% | 5.704 | 9.8% |
| Chelsea city | 40,130 | −1.5% | 2.219 | 3.8% |
| Winthrop Town city | 18,647 | −3.5% | 1.994 | 3.4% |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Suffolk County. Land: 2026 Census Gazetteer. How communities are listed.
Metropolitan area
Suffolk County is a central county of the Boston-Cambridge-Newton, MA-NH Metropolitan Statistical Area, in the Boston, MA metropolitan division. Its 7 county equivalents have 5,034,221 residents on 3,486.3 square miles of land; Suffolk County accounts for 1.7% of the land and 15.7% of the residents. By combined land it ranks #84 of 393 metropolitan areas, and #11 by population. It belongs to the Boston-Worcester-Providence, MA-RI-NH Combined Statistical Area.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| Middlesex County | 1,669,979 | 817.9 |
| Essex County | 826,653 | 492.5 |
| Suffolk County | 791,891 | 58.3 |
| Norfolk County | 739,749 | 396.1 |
| Plymouth County | 546,829 | 658.5 |
| Rockingham CountyNew Hampshire | 324,077 | 695.6 |
| Strafford CountyNew Hampshire | 135,043 | 367.5 |
ZIP codes
39 ZIP Code Tabulation Areas have land in Suffolk County; 35 of them have most of their land inside the county, and the others mainly cover neighboring areas.
021080210902110021110211302114021150211602118021190212002121021220212402125021260212702128021290213002131021320213302134021350213602149021500215102152021630219902203022050221002215024450244602467
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 Suffolk County
Suffolk County shares a land border with 3 county equivalents. Each of them has more land than Suffolk County. The largest neighbor is Middlesex County (817.9 mi²) and the smallest is Norfolk County (396.1 mi²). Together with its neighbors, Suffolk County forms a block of 1,764.8 mi² of land, of which it holds 3.3%.
| Bordering county equivalent | Land mi² | Size vs. Suffolk | Compare |
|---|---|---|---|
| Middlesex County | 817.9 | 14× larger | Compare |
| Essex County | 492.5 | 8.5× larger | Compare |
| Norfolk County | 396.1 | 6.8× larger | Compare |
How big is Suffolk County compared with U.S. states?
Suffolk County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 18 times as much. Massachusetts’s county land could hold about 134 areas the size of Suffolk County.
Another way to picture it: the same land area would fill a square about 7.63 miles (12.3 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 Suffolk County?
Suffolk County has more land than 103 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 Suffolk County at #3,096 nationally by total area, 23 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 51.5%, compared with a national county-equivalent median of 1.2% — 50.4 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 Suffolk County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #3118 | Caguas Municipio, Puerto Rico | 58.6 | Compare |
| #3119 | Suffolk County, Massachusetts | 58.3 | This county |
| #3120 | Richmond County, New York | 57.5 | 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 42.332735, -71.013513. 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: 150,886,864 m²; AWATER: 160,489,722 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 Suffolk County?
Suffolk County, Massachusetts has 58.3 square miles (150.9 km²) of land and 62 square miles of water, for a total area of 120.2 square miles. It ranks #3119 of 3,222 U.S. county equivalents by land area.
Is Suffolk County the largest county in Massachusetts?
No. Suffolk County ranks #13 of 14 in Massachusetts by land area. The largest is Worcester County, with 1,510.7 square miles of land.
What counties border Suffolk County?
Suffolk County shares a land border with Middlesex County, Norfolk County, and Essex County.
What is the population of Suffolk County?
The Census Bureau estimates Suffolk County had 791,891 residents on July 1, 2025, ranking #85 of 3,222 county equivalents. That is 13,593 people per square mile of land.
What is the county seat of Suffolk County?
The county seat of Suffolk County is Boston.
What cities and towns are in Suffolk County?
Suffolk County has 4 county subdivisions (cities, towns and townships). The most populous are Boston city, Revere city, Chelsea city, and Winthrop Town city.
Is Suffolk County part of a metropolitan area?
Yes. It is a central county of the Boston-Cambridge-Newton, MA-NH Metropolitan Statistical Area, which has 7 county equivalents and 5,034,221 residents.
How many ZIP codes are in Suffolk County?
39 ZIP Code Tabulation Areas have land in Suffolk County, and 35 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Suffolk County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 17.7 times as much land.
How many acres of land are in Suffolk County?
The land measurement converts to approximately 37,285 acres. Including water, total area is approximately 76,943 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.