The map above shows Illinois and South Dakota side by side at exactly the same scale, using equal-area projections, so their true relative sizes are preserved.
Illinois vs South Dakota Geography
Land area: Illinois has a land area of 55,513 square miles (143,778 km²), while South Dakota has 75,808 square miles (196,342 km²). South Dakota's land area is 1.4 times (37%) larger than Illinois'.
Total area: Illinois: 57,913 square miles (149,995 km²) vs South Dakota: 77,116 square miles (199,729 km²), including inland and coastal water. South Dakota's total area is 1.3 times (33%) larger than Illinois'.
Length: Illinois is 390 miles (628 km) long from north to south; South Dakota is 443 miles (712 km). South Dakota's north-south length is 1.1 times (14%) longer than Illinois'.
Width: Illinois spans 283 miles (456 km) east to west; South Dakota spans 371 miles (597 km). South Dakota's east-west width is 1.3 times (31%) wider than Illinois'.
Highest point: Illinois's highest point is Charles Mound at 1,232 feet (376 m); South Dakota's is Black Elk Peak at 7,198 feet (2,194 m). Black Elk Peak is 5,966 feet higher than Charles Mound.
Lowest point: Illinois's lowest point is Mississippi River at 292 feet; South Dakota's is Big Stone Lake at 966 feet. Illinois's lowest point is 674 feet lower.
Illinois vs South Dakota Population and History
Population: Illinois has a population of 12,710,158 (2024), while South Dakota has 924,669 (2024). Illinois' population is 13.7 times larger than South Dakota's.
Population density: Illinois: 229.0 people per square mile vs South Dakota: 12.2. Illinois' population density is 18.8 times higher than South Dakota's.
Biggest city: Illinois's biggest city is Chicago with 2,721,308 people; South Dakota's is Sioux Falls with 209,289. Chicago's population is 13.0 times larger than Sioux Falls'.
Largest metro area: Illinois's largest metropolitan area is Chicago-Naperville-Elgin, IL-IN metro area (9,408,576 people) vs South Dakota's Sioux Falls, SD-MN metro area (308,266). Chicago-Naperville-Elgin, IL-IN metro area's population is 30.5 times larger than Sioux Falls, SD-MN metro area's.
History: Illinois: Admitted to the Union on December 3, 1818, as the 21st state. South Dakota: Admitted to the Union on November 2, 1889, as the 40th state. In its current form, Illinois is the older of the two by 71 years.
Illinois vs South Dakota Economy
GDP: Illinois's GDP is $1,148.1 billion (2024) vs South Dakota's $76.8 billion. Illinois' economic output is 14.9 times larger than South Dakota's.
GDP per capita: Illinois: $90,330 per person vs South Dakota: $83,052. Illinois' GDP per capita is 1.1 times (9%) higher than South Dakota's.
Average income: Illinois: $74,522 vs South Dakota: $75,699 average income per person (per capita personal income). Illinois and South Dakota have about the same average income.
Illinois vs South Dakota Counties
Number of counties: Illinois has 102 counties, while South Dakota has 66. Illinois' county count is 1.5 times (55%) higher than South Dakota's.
Biggest county by area: Illinois's largest county is McLean County at 1,183 square miles; South Dakota's is Meade County at 3,471 square miles. Meade County's land area is 2.9 times (193%) larger than McLean County's.
Smallest county by area: Illinois: Putnam County (160 sq mi) vs South Dakota: Clay County (412 sq mi). Clay County's land area is 2.6 times (157%) larger than Putnam County's.
Most populous county: Illinois: Cook County (5,182,617 people) vs South Dakota: Minnehaha County (208,639 people). Cook County's population is 24.8 times larger than Minnehaha County's.
Least populous county: Illinois: Hardin County (3,550 people) vs South Dakota: Jones County (874 people). Hardin County's population is 4.1 times (306%) larger than Jones County's.
Richest county: Illinois: Cumberland County ($104,890 per capita income) vs South Dakota: Union County ($146,712). Union County's income is 1.4 times (40%) richer than Cumberland County's.
Poorest county: Illinois: Lawrence County ($43,606 per capita income) vs South Dakota: Ziebach County ($32,778). Lawrence County's income is 1.3 times (33%) richer than Ziebach County's.
Illinois vs South Dakota Taxes
State income tax: Illinois has a top income tax rate of 4.95%, while South Dakota has no state income tax. Illinois's top rate is 4.95 percentage points higher.
Property tax: Illinois: 1.92% effective rate vs South Dakota: 1.02% of home value per year. Illinois's rate is 0.9 percentage points higher.
Sales tax: Illinois: 8.98% combined state and average local rate vs South Dakota: 6.11%. Illinois's combined rate is 2.87 percentage points higher.
Official Websites
Illinois official website · South Dakota official website
More Size Comparisons
All Illinois size comparisons · All South Dakota size comparisons
Area, elevation and boundary figures come from official national statistics and US Census Bureau and Natural Earth boundary data; US state population, economic, county and tax figures come from the US Census Bureau, the Bureau of Economic Analysis and the Tax Foundation. Figures are rounded and for general reference.