The map above shows Illinois and Montana side by side at exactly the same scale, using equal-area projections, so their true relative sizes are preserved.
Illinois vs Montana Geography
Land area: Illinois has a land area of 55,513 square miles (143,778 km²), while Montana has 145,550 square miles (376,973 km²). Montana's land area is 2.6 times (162%) larger than Illinois'.
Total area: Illinois: 57,913 square miles (149,995 km²) vs Montana: 147,043 square miles (380,840 km²), including inland and coastal water. Montana's total area is 2.5 times (154%) larger than Illinois'.
Length: Illinois is 390 miles (628 km) long from north to south; Montana is 319 miles (514 km). Illinois' north-south length is 1.2 times (22%) longer than Montana's.
Width: Illinois spans 283 miles (456 km) east to west; Montana spans 607 miles (976 km). Montana's east-west width is 2.1 times (114%) wider than Illinois'.
Highest point: Illinois's highest point is Charles Mound at 1,232 feet (376 m); Montana's is Granite Peak at 12,767 feet (3,891 m). Granite Peak is 11,535 feet higher than Charles Mound.
Lowest point: Illinois's lowest point is Mississippi River at 292 feet; Montana's is Kootenai River at 1,805 feet. Illinois's lowest point is 1,513 feet lower.
Illinois vs Montana Population and History
Population: Illinois has a population of 12,710,158 (2024), while Montana has 1,137,233 (2024). Illinois' population is 11.2 times larger than Montana's.
Population density: Illinois: 229.0 people per square mile vs Montana: 7.8. Illinois' population density is 29.4 times higher than Montana's.
Biggest city: Illinois's biggest city is Chicago with 2,721,308 people; Montana's is Billings with 121,483. Chicago's population is 22.4 times larger than Billings'.
Largest metro area: Illinois's largest metropolitan area is Chicago-Naperville-Elgin, IL-IN metro area (9,408,576 people) vs Montana's Billings, MT metro area (192,531). Chicago-Naperville-Elgin, IL-IN metro area's population is 48.9 times larger than Billings, MT metro area's.
History: Illinois: Admitted to the Union on December 3, 1818, as the 21st state. Montana: Admitted to the Union on November 8, 1889, as the 41st state. In its current form, Illinois is the older of the two by 71 years.
Illinois vs Montana Economy
GDP: Illinois's GDP is $1,148.1 billion (2024) vs Montana's $78.4 billion. Illinois' economic output is 14.6 times larger than Montana's.
GDP per capita: Illinois: $90,330 per person vs Montana: $68,975. Illinois' GDP per capita is 1.3 times (31%) higher than Montana's.
Average income: Illinois: $74,522 vs Montana: $69,240 average income per person (per capita personal income). Illinois' average income is 1.1 times (8%) higher than Montana's.
Illinois vs Montana Counties
Number of counties: Illinois has 102 counties, while Montana has 56. Illinois' county count is 1.8 times (82%) higher than Montana's.
Biggest county by area: Illinois's largest county is McLean County at 1,183 square miles; Montana's is Beaverhead County at 5,543 square miles. Beaverhead County's land area is 4.7 times (368%) larger than McLean County's.
Smallest county by area: Illinois: Putnam County (160 sq mi) vs Montana: Silver Bow County (718 sq mi). Silver Bow County's land area is 4.5 times (348%) larger than Putnam County's.
Most populous county: Illinois: Cook County (5,182,617 people) vs Montana: Yellowstone County (171,583 people). Cook County's population is 30.2 times larger than Yellowstone County's.
Least populous county: Illinois: Hardin County (3,550 people) vs Montana: Petroleum County (525 people). Hardin County's population is 6.8 times (576%) larger than Petroleum County's.
Richest county: Illinois: Cumberland County ($104,890 per capita income) vs Montana: Gallatin County ($94,573). Cumberland County's income is 1.1 times (11%) richer than Gallatin County's.
Poorest county: Illinois: Lawrence County ($43,606 per capita income) vs Montana: Blaine County ($37,554). Lawrence County's income is 1.2 times (16%) richer than Blaine County's.
Illinois vs Montana Taxes
State income tax: Illinois has a top income tax rate of 4.95%, while Montana has a top income tax rate of 5.65%. Montana's top rate is 0.7 percentage points higher.
Property tax: Illinois: 1.92% effective rate vs Montana: 0.69% of home value per year. Illinois's rate is 1.23 percentage points higher.
Sales tax: Illinois: 8.98% combined state and average local rate vs Montana: 0%. Illinois's combined rate is 8.98 percentage points higher.
Official Websites
Illinois official website · Montana official website
More Size Comparisons
All Illinois size comparisons · All Montana 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.