The map above shows Colorado and Illinois side by side at exactly the same scale, using equal-area projections, so their true relative sizes are preserved.
Colorado vs Illinois Geography
Land area: Colorado has a land area of 103,637 square miles (268,419 km²), while Illinois has 55,513 square miles (143,778 km²). Colorado's land area is 1.9 times (87%) larger than Illinois'.
Total area: Colorado: 104,095 square miles (269,605 km²) vs Illinois: 57,913 square miles (149,995 km²), including inland and coastal water. Colorado's total area is 1.8 times (80%) larger than Illinois'.
Length: Colorado is 467 miles (751 km) long from north to south; Illinois is 390 miles (628 km). Colorado's north-south length is 1.2 times (20%) longer than Illinois'.
Width: Colorado spans 387 miles (622 km) east to west; Illinois spans 283 miles (456 km). Colorado's east-west width is 1.4 times (37%) wider than Illinois'.
Highest point: Colorado's highest point is Mount Elbert at 14,422 feet (4,396 m); Illinois's is Charles Mound at 1,232 feet (376 m). Mount Elbert is 13,190 feet higher than Charles Mound.
Lowest point: Colorado's lowest point is Arikaree River at 3,326 feet; Illinois's is Mississippi River at 292 feet. Illinois's lowest point is 3,034 feet lower.
Colorado vs Illinois Population and History
Population: Colorado has a population of 5,957,493 (2024), while Illinois has 12,710,158 (2024). Illinois' population is 2.1 times (113%) larger than Colorado's.
Population density: Colorado: 57.5 people per square mile vs Illinois: 229.0. Illinois' population density is 4.0 times (298%) higher than Colorado's.
Biggest city: Colorado's biggest city is Denver with 729,019 people; Illinois's is Chicago with 2,721,308. Chicago's population is 3.7 times (273%) larger than Denver's.
Largest metro area: Colorado's largest metropolitan area is Denver-Aurora-Centennial, CO metro area (3,052,498 people) vs Illinois's Chicago-Naperville-Elgin, IL-IN metro area (9,408,576). Chicago-Naperville-Elgin, IL-IN metro area's population is 3.1 times (208%) larger than Denver-Aurora-Centennial, CO metro area's.
History: Colorado: Admitted to the Union on August 1, 1876, as the 38th state. Illinois: Admitted to the Union on December 3, 1818, as the 21st state. In its current form, Illinois is the older of the two by 58 years.
Colorado vs Illinois Economy
GDP: Colorado's GDP is $557.6 billion (2024) vs Illinois's $1,148.1 billion. Illinois' economic output is 2.1 times (106%) larger than Colorado's.
GDP per capita: Colorado: $93,602 per person vs Illinois: $90,330. Colorado and Illinois have about the same GDP per capita.
Average income: Colorado: $83,055 vs Illinois: $74,522 average income per person (per capita personal income). Colorado's average income is 1.1 times (11%) higher than Illinois'.
Colorado vs Illinois Counties
Number of counties: Colorado has 64 counties, while Illinois has 102. Illinois' county count is 1.6 times (59%) higher than Colorado's.
Biggest county by area: Colorado's largest county is Las Animas County at 4,773 square miles; Illinois's is McLean County at 1,183 square miles. Las Animas County's land area is 4.0 times (303%) larger than McLean County's.
Smallest county by area: Colorado: Broomfield County (33 sq mi) vs Illinois: Putnam County (160 sq mi). Putnam County's land area is 4.9 times (385%) larger than Broomfield County's.
Most populous county: Colorado: El Paso County (752,772 people) vs Illinois: Cook County (5,182,617 people). Cook County's population is 6.9 times (588%) larger than El Paso County's.
Least populous county: Colorado: Hinsdale County (747 people) vs Illinois: Hardin County (3,550 people). Hardin County's population is 4.8 times (375%) larger than Hinsdale County's.
Richest county: Colorado: Pitkin County ($275,044 per capita income) vs Illinois: Cumberland County ($104,890). Pitkin County's income is 2.6 times (162%) richer than Cumberland County's.
Poorest county: Colorado: Crowley County ($27,232 per capita income) vs Illinois: Lawrence County ($43,606). Lawrence County's income is 1.6 times (60%) richer than Crowley County's.
Colorado vs Illinois Taxes
State income tax: Colorado has a top income tax rate of 4.4%, while Illinois has a top income tax rate of 4.95%. Illinois's top rate is 0.55 percentage points higher.
Property tax: Colorado: 0.49% effective rate vs Illinois: 1.92% of home value per year. Illinois's rate is 1.43 percentage points higher.
Sales tax: Colorado: 7.89% combined state and average local rate vs Illinois: 8.98%. Illinois's combined rate is 1.09 percentage points higher.
Official Websites
Colorado official website · Illinois official website
More Size Comparisons
All Colorado size comparisons · All Illinois 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.