The map above shows Illinois and Oklahoma side by side at exactly the same scale, using equal-area projections, so their true relative sizes are preserved.
Illinois vs Oklahoma Geography
Land area: Illinois has a land area of 55,513 square miles (143,778 km²), while Oklahoma has 68,597 square miles (177,665 km²). Oklahoma's land area is 1.2 times (24%) larger than Illinois'.
Total area: Illinois: 57,913 square miles (149,995 km²) vs Oklahoma: 69,899 square miles (181,038 km²), including inland and coastal water. Oklahoma's total area is 1.2 times (21%) larger than Illinois'.
Length: Illinois is 390 miles (628 km) long from north to south; Oklahoma is 533 miles (857 km). Oklahoma's north-south length is 1.4 times (37%) longer than Illinois'.
Width: Illinois spans 283 miles (456 km) east to west; Oklahoma spans 490 miles (789 km). Oklahoma's east-west width is 1.7 times (73%) wider than Illinois'.
Highest point: Illinois's highest point is Charles Mound at 1,232 feet (376 m); Oklahoma's is Black Mesa at 4,980 feet (1,518 m). Black Mesa is 3,748 feet higher than Charles Mound.
Lowest point: Illinois's lowest point is Mississippi River at 292 feet; Oklahoma's is Little River at 289 feet. Oklahoma's lowest point is 3 feet lower.
Illinois vs Oklahoma Population and History
Population: Illinois has a population of 12,710,158 (2024), while Oklahoma has 4,095,393 (2024). Illinois' population is 3.1 times (210%) larger than Oklahoma's.
Population density: Illinois: 229.0 people per square mile vs Oklahoma: 59.7. Illinois' population density is 3.8 times (284%) higher than Oklahoma's.
Biggest city: Illinois's biggest city is Chicago with 2,721,308 people; Oklahoma's is Oklahoma City with 712,919. Chicago's population is 3.8 times (282%) larger than Oklahoma City's.
Largest metro area: Illinois's largest metropolitan area is Chicago-Naperville-Elgin, IL-IN metro area (9,408,576 people) vs Oklahoma's Oklahoma City, OK metro area (1,497,821). Chicago-Naperville-Elgin, IL-IN metro area's population is 6.3 times (528%) larger than Oklahoma City, OK metro area's.
History: Illinois: Admitted to the Union on December 3, 1818, as the 21st state. Oklahoma: Admitted to the Union on November 16, 1907, as the 46th state. In its current form, Illinois is the older of the two by 89 years.
Illinois vs Oklahoma Economy
GDP: Illinois's GDP is $1,148.1 billion (2024) vs Oklahoma's $263.7 billion. Illinois' economic output is 4.4 times (335%) larger than Oklahoma's.
GDP per capita: Illinois: $90,330 per person vs Oklahoma: $64,388. Illinois' GDP per capita is 1.4 times (40%) higher than Oklahoma's.
Average income: Illinois: $74,522 vs Oklahoma: $63,708 average income per person (per capita personal income). Illinois' average income is 1.2 times (17%) higher than Oklahoma's.
Illinois vs Oklahoma Counties
Number of counties: Illinois has 102 counties, while Oklahoma has 77. Illinois' county count is 1.3 times (32%) higher than Oklahoma's.
Biggest county by area: Illinois's largest county is McLean County at 1,183 square miles; Oklahoma's is Osage County at 2,247 square miles. Osage County's land area is 1.9 times (90%) larger than McLean County's.
Smallest county by area: Illinois: Putnam County (160 sq mi) vs Oklahoma: Marshall County (372 sq mi). Marshall County's land area is 2.3 times (132%) larger than Putnam County's.
Most populous county: Illinois: Cook County (5,182,617 people) vs Oklahoma: Oklahoma County (816,490 people). Cook County's population is 6.3 times (535%) larger than Oklahoma County's.
Least populous county: Illinois: Hardin County (3,550 people) vs Oklahoma: Cimarron County (2,133 people). Hardin County's population is 1.7 times (66%) larger than Cimarron County's.
Richest county: Illinois: Cumberland County ($104,890 per capita income) vs Oklahoma: Washington County ($126,749). Washington County's income is 1.2 times (21%) richer than Cumberland County's.
Poorest county: Illinois: Lawrence County ($43,606 per capita income) vs Oklahoma: Atoka County ($38,709). Lawrence County's income is 1.1 times (13%) richer than Atoka County's.
Illinois vs Oklahoma Taxes
State income tax: Illinois has a top income tax rate of 4.95%, while Oklahoma has a top income tax rate of 4.5%. Illinois's top rate is 0.45 percentage points higher.
Property tax: Illinois: 1.92% effective rate vs Oklahoma: 0.75% of home value per year. Illinois's rate is 1.17 percentage points higher.
Sales tax: Illinois: 8.98% combined state and average local rate vs Oklahoma: 9.06%. Oklahoma's combined rate is 0.08 percentage points higher.
Official Websites
Illinois official website · Oklahoma official website
More Size Comparisons
All Illinois size comparisons · All Oklahoma 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.