County outline
Where Sanilac County is located
Area breakdown
Land accounts for 60.5% of Sanilac County’s measured area and water for 39.5%. Its combined area converts to 4,117.9 square kilometers or approximately 1,017,562 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 962.571 | 2,493.047 | 616,045.4 |
| Water | 627.369 | 1,624.878 | 401,516.2 |
| Total | 1,589.94 | 4,117.926 | 1,017,561.6 |
How Sanilac County compares
By original Census land area, Sanilac County ranks #11 of 83 in Michigan and #729 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.695 times the Michigan county-equivalent median of 567.8 square miles. It accounts for 1.7% of the combined county land area in the state.
See the complete Michigan ranking · What counts as a county equivalent?
Population and density of Sanilac County
The Census Bureau estimates that 40,083 people lived in Sanilac County on July 1, 2025. That ranks #1,210 of 3,222 county equivalents nationally and #41 of 83 in Michigan. Since the April 1, 2020 estimates base of 40,611, the population has declined by 528 (−1.3%), compared with +0.5% for Michigan as a whole.
With 962.6 square miles of land, that is 42 people per square mile (16 per km²), placing Sanilac County #1,717 nationally for density and #55 in Michigan. The median county equivalent has 47 people per square mile; the Michigan median is 62. Put another way, there are about 15 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 40,499 | 40,536 | 40,506 | 40,389 | 40,238 | 40,083 |
| Change | — | +37 | −30 | −117 | −151 | −155 |
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 Sanilac County
Sanilac County is divided into 30 municipalities and townships. In Michigan, county subdivisions are local governments, and together they cover all of the county’s land and residents.
The most populous is Lexington township, with 3,452 residents (8.6% of the county). The largest by land is Marlette township, at 52.5 mi², or 5.4% of the county’s land. The county seat, Sandusky city, has 2,664 residents.
| County subdivision | Population 2025 | Since 2020 | Land mi² | Share of county land |
|---|---|---|---|---|
| Lexington township | 3,452 | −0.9% | 36 | 3.7% |
| Worth township | 3,423 | −1.5% | 38.6 | 4% |
| Sandusky cityCounty seat | 2,664 | −1.7% | 2.147 | 0.2% |
| Sanilac township | 2,281 | −0.8% | 40.8 | 4.2% |
| Croswell city | 2,263 | −1.9% | 2.357 | 0.2% |
| Marlette city | 1,833 | −1.2% | 1.615 | 0.2% |
| Marlette township | 1,656 | −1.5% | 52.5 | 5.4% |
| Marion township | 1,547 | −1.6% | 36.1 | 3.7% |
| Washington township | 1,514 | −1.1% | 36 | 3.7% |
| Elk township | 1,498 | −1.5% | 35.7 | 3.7% |
| Speaker township | 1,330 | −1.2% | 34.6 | 3.6% |
| Brown City city | 1,277 | −1.8% | 1.094 | 0.1% |
| Watertown township | 1,241 | −1.4% | 35.1 | 3.6% |
| Maple Valley township | 1,161 | −1.5% | 34.5 | 3.6% |
| Buel township | 1,153 | −0.5% | 37.6 | 3.9% |
Show the other 15 subdivisions
| Name | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Moore township | 1,092 | −1% | 36.3 |
| Flynn township | 991 | −1.4% | 35.8 |
| Evergreen township | 952 | −1.3% | 35.4 |
| Fremont township | 950 | −1.3% | 35 |
| Custer township | 902 | +0.4% | 35.3 |
| Forester township | 871 | −1.1% | 25.2 |
| Greenleaf township | 810 | −1.1% | 35.9 |
| Delaware township | 772 | −1.4% | 46.4 |
| Lamotte township | 763 | −1.3% | 35.5 |
| Bridgehampton township | 737 | −0.7% | 36.1 |
| Elmer township | 711 | −1.7% | 36.3 |
| Argyle township | 677 | −1.7% | 36.3 |
| Austin township | 608 | −1.5% | 36.2 |
| Minden township | 541 | −1.8% | 36.1 |
| Wheatland township | 413 | −1.7% | 36.3 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Sanilac County. Land: 2026 Census Gazetteer. How communities are listed.
Metropolitan area
Sanilac County is not part of any metropolitan or micropolitan statistical area in the Office of Management and Budget’s July 2023 delineation; 1,306 other county equivalents are also outside one. These areas are built around an urban core of at least 10,000 people plus the counties tied to it by commuting, so counties outside them are generally rural.
ZIP codes
23 ZIP Code Tabulation Areas have land in Sanilac County; 18 of them have most of their land inside the county, and the others mainly cover neighboring areas.
4803248097484014841048416484194842248426484274843448441484504845348454484564846548466484694847048471484724847548726
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 Sanilac County
Sanilac County shares a land border with 4 county equivalents. It has more land than every one of them. The largest neighbor is Huron County (835.9 mi²) and the smallest is Lapeer County (647.5 mi²). Together with its neighbors, Sanilac County forms a block of 3,972.4 mi² of land, of which it holds 24.2%.
| Bordering county equivalent | Land mi² | Size vs. Sanilac | Compare |
|---|---|---|---|
| Huron County | 835.9 | 1.2× smaller | Compare |
| Tuscola County | 804.9 | 1.2× smaller | Compare |
| St. Clair County | 721.5 | 1.3× smaller | Compare |
| Lapeer County | 647.5 | 1.5× smaller | Compare |
How big is Sanilac County compared with U.S. states?
Sanilac 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. Michigan’s county land could hold about 59 areas the size of Sanilac County.
Another way to picture it: the same land area would fill a square about 31 miles (49.9 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 Sanilac County?
Sanilac County has more land than 2,493 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 Sanilac County at #423 nationally by total area, 306 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 39.5%, compared with a national county-equivalent median of 1.2% — 38.3 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 Sanilac County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #728 | Sacramento County, California | 965.4 | Compare |
| #729 | Sanilac County, Michigan | 962.6 | This county |
| #730 | Colorado County, Texas | 960.3 | 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 43.449155, -82.642815. 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: 2,493,048,516 m²; AWATER: 1,624,879,474 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 Sanilac County?
Sanilac County, Michigan has 962.6 square miles (2,493 km²) of land and 627.4 square miles of water, for a total area of 1,589.9 square miles. It ranks #729 of 3,222 U.S. county equivalents by land area.
Is Sanilac County the largest county in Michigan?
No. Sanilac County ranks #11 of 83 in Michigan by land area. The largest is Marquette County, with 1,809.1 square miles of land.
What counties border Sanilac County?
Sanilac County shares a land border with Huron County, St. Clair County, Tuscola County, and Lapeer County.
What is the population of Sanilac County?
The Census Bureau estimates Sanilac County had 40,083 residents on July 1, 2025, ranking #1,210 of 3,222 county equivalents. That is 42 people per square mile of land.
What is the county seat of Sanilac County?
The county seat of Sanilac County is Sandusky.
What cities and towns are in Sanilac County?
Sanilac County has 30 county subdivisions (cities, towns and townships). The most populous five are Lexington township, Worth township, Sandusky city, Sanilac township, and Croswell city.
Is Sanilac County part of a metropolitan area?
No. Sanilac County is outside every metropolitan and micropolitan statistical area in the July 2023 OMB delineation.
How many ZIP codes are in Sanilac County?
23 ZIP Code Tabulation Areas have land in Sanilac County, and 18 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Sanilac 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 Sanilac County?
The land measurement converts to approximately 616,045 acres. Including water, total area is approximately 1,017,562 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.