The map above shows Idaho and Illinois side by side at exactly the same scale, using equal-area projections, so their true relative sizes are preserved.
Idaho vs Illinois Geography
Land area: Idaho has a land area of 82,645 square miles (214,051 km²), while Illinois has 55,513 square miles (143,778 km²). Idaho's land area is 1.5 times (49%) larger than Illinois'.
Total area: Idaho: 83,569 square miles (216,441 km²) vs Illinois: 57,913 square miles (149,995 km²), including inland and coastal water. Idaho's total area is 1.4 times (44%) larger than Illinois'.
Length: Idaho is 483 miles (778 km) long from north to south; Illinois is 390 miles (628 km). Idaho's north-south length is 1.2 times (24%) longer than Illinois'.
Width: Idaho spans 352 miles (566 km) east to west; Illinois spans 283 miles (456 km). Idaho's east-west width is 1.2 times (24%) wider than Illinois'.
Highest point: Idaho's highest point is Borah Peak at 12,631 feet (3,850 m); Illinois's is Charles Mound at 1,232 feet (376 m). Borah Peak is 11,399 feet higher than Charles Mound.
Lowest point: Idaho's lowest point is Snake River at 718 feet; Illinois's is Mississippi River at 292 feet. Illinois's lowest point is 426 feet lower.
Idaho vs Illinois Population and History
Population: Idaho has a population of 2,001,619 (2024), while Illinois has 12,710,158 (2024). Illinois' population is 6.3 times (535%) larger than Idaho's.
Population density: Idaho: 24.2 people per square mile vs Illinois: 229.0. Illinois' population density is 9.5 times (846%) higher than Idaho's.
Biggest city: Idaho's biggest city is Boise with 237,963 people; Illinois's is Chicago with 2,721,308. Chicago's population is 11.4 times larger than Boise's.
Largest metro area: Idaho's largest metropolitan area is Boise City, ID metro area (845,877 people) vs Illinois's Chicago-Naperville-Elgin, IL-IN metro area (9,408,576). Chicago-Naperville-Elgin, IL-IN metro area's population is 11.1 times larger than Boise City, ID metro area's.
History: Idaho: Admitted to the Union on July 3, 1890, as the 43rd 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 72 years.
Idaho vs Illinois Economy
GDP: Idaho's GDP is $129.0 billion (2024) vs Illinois's $1,148.1 billion. Illinois' economic output is 8.9 times (790%) larger than Idaho's.
GDP per capita: Idaho: $64,457 per person vs Illinois: $90,330. Illinois' GDP per capita is 1.4 times (40%) higher than Idaho's.
Average income: Idaho: $62,323 vs Illinois: $74,522 average income per person (per capita personal income). Illinois' average income is 1.2 times (20%) higher than Idaho's.
Idaho vs Illinois Counties
Number of counties: Idaho has 44 counties, while Illinois has 102. Illinois' county count is 2.3 times (132%) higher than Idaho's.
Biggest county by area: Idaho's largest county is Idaho County at 8,478 square miles; Illinois's is McLean County at 1,183 square miles. Idaho County's land area is 7.2 times (616%) larger than McLean County's.
Smallest county by area: Idaho: Payette County (407 sq mi) vs Illinois: Putnam County (160 sq mi). Payette County's land area is 2.5 times (154%) larger than Putnam County's.
Most populous county: Idaho: Ada County (535,799 people) vs Illinois: Cook County (5,182,617 people). Cook County's population is 9.7 times (867%) larger than Ada County's.
Least populous county: Idaho: Clark County (794 people) vs Illinois: Hardin County (3,550 people). Hardin County's population is 4.5 times (347%) larger than Clark County's.
Richest county: Idaho: Blaine County ($202,612 per capita income) vs Illinois: Cumberland County ($104,890). Blaine County's income is 1.9 times (93%) richer than Cumberland County's.
Poorest county: Idaho: Madison County ($29,485 per capita income) vs Illinois: Lawrence County ($43,606). Lawrence County's income is 1.5 times (48%) richer than Madison County's.
Idaho vs Illinois Taxes
State income tax: Idaho has a top income tax rate of 5.3%, while Illinois has a top income tax rate of 4.95%. Idaho's top rate is 0.35 percentage points higher.
Property tax: Idaho: 0.43% effective rate vs Illinois: 1.92% of home value per year. Illinois's rate is 1.49 percentage points higher.
Sales tax: Idaho: 6.03% combined state and average local rate vs Illinois: 8.98%. Illinois's combined rate is 2.95 percentage points higher.
Official Websites
Idaho official website · Illinois official website
More Size Comparisons
All Idaho 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.