The map above shows Connecticut and Illinois side by side at exactly the same scale, using equal-area projections, so their true relative sizes are preserved.
Connecticut vs Illinois Geography
Land area: Connecticut has a land area of 4,843 square miles (12,542 km²), while Illinois has 55,513 square miles (143,778 km²). Illinois' land area is 11.5 times larger than Connecticut's.
Total area: Connecticut: 5,544 square miles (14,358 km²) vs Illinois: 57,913 square miles (149,995 km²), including inland and coastal water. Illinois' total area is 10.4 times larger than Connecticut's.
Length: Connecticut is 73 miles (118 km) long from north to south; Illinois is 390 miles (628 km). Illinois' north-south length is 5.3 times (434%) longer than Connecticut's.
Width: Connecticut spans 104 miles (167 km) east to west; Illinois spans 283 miles (456 km). Illinois' east-west width is 2.7 times (172%) wider than Connecticut's.
Highest point: Connecticut's highest point is Mount Frissell (south slope) at 2,376 feet (724 m); Illinois's is Charles Mound at 1,232 feet (376 m). Mount Frissell (south slope) is 1,144 feet higher than Charles Mound.
Lowest point: Connecticut's lowest point is Long Island Sound at 0 feet; Illinois's is Mississippi River at 292 feet. Connecticut's lowest point is 292 feet lower.
Connecticut vs Illinois Population and History
Population: Connecticut has a population of 3,675,069 (2024), while Illinois has 12,710,158 (2024). Illinois' population is 3.5 times (246%) larger than Connecticut's.
Population density: Connecticut: 758.9 people per square mile vs Illinois: 229.0. Connecticut's population density is 3.3 times (231%) higher than Illinois'.
Biggest city: Connecticut's biggest city is Bridgeport with 151,599 people; Illinois's is Chicago with 2,721,308. Chicago's population is 18.0 times larger than Bridgeport's.
Largest metro area: Connecticut's largest metropolitan area is Hartford-West Hartford-East Hartford, CT metro area (1,169,048 people) vs Illinois's Chicago-Naperville-Elgin, IL-IN metro area (9,408,576). Chicago-Naperville-Elgin, IL-IN metro area's population is 8.0 times (705%) larger than Hartford-West Hartford-East Hartford, CT metro area's.
History: Connecticut: Admitted to the Union on January 9, 1788, as the 5th state. Illinois: Admitted to the Union on December 3, 1818, as the 21st state. In its current form, Connecticut is the older of the two by 30 years.
Connecticut vs Illinois Economy
GDP: Connecticut's GDP is $356.8 billion (2024) vs Illinois's $1,148.1 billion. Illinois' economic output is 3.2 times (222%) larger than Connecticut's.
GDP per capita: Connecticut: $97,096 per person vs Illinois: $90,330. Connecticut's GDP per capita is 1.1 times (7%) higher than Illinois'.
Average income: Connecticut: $95,067 vs Illinois: $74,522 average income per person (per capita personal income). Connecticut's average income is 1.3 times (28%) higher than Illinois'.
Connecticut vs Illinois Counties
Number of counties: Connecticut has 9 counties, while Illinois has 102. Illinois' county count is 11.3 times higher than Connecticut's.
Biggest county by area: Connecticut's largest county is Capitol Planning Region at 1,027 square miles; Illinois's is McLean County at 1,183 square miles. McLean County's land area is 1.2 times (15%) larger than Capitol Planning Region's.
Smallest county by area: Connecticut: Greater Bridgeport Planning Region (140 sq mi) vs Illinois: Putnam County (160 sq mi). Putnam County's land area is 1.1 times (14%) larger than Greater Bridgeport Planning Region's.
Most populous county: Connecticut: Capitol Planning Region (991,508 people) vs Illinois: Cook County (5,182,617 people). Cook County's population is 5.2 times (423%) larger than Capitol Planning Region's.
Least populous county: Connecticut: Northeastern Connecticut Planning Region (97,701 people) vs Illinois: Hardin County (3,550 people). Northeastern Connecticut Planning Region's population is 27.5 times larger than Hardin County's.
Richest county: Connecticut: Western Connecticut Planning Region ($165,513 per capita income) vs Illinois: Cumberland County ($104,890). Western Connecticut Planning Region's income is 1.6 times (58%) richer than Cumberland County's.
Poorest county: Connecticut: Southeastern Connecticut Planning Region ($64,845 per capita income) vs Illinois: Lawrence County ($43,606). Southeastern Connecticut Planning Region's income is 1.5 times (49%) richer than Lawrence County's.
Connecticut vs Illinois Taxes
State income tax: Connecticut has a top income tax rate of 6.99%, while Illinois has a top income tax rate of 4.95%. Connecticut's top rate is 2.04 percentage points higher.
Property tax: Connecticut: 1.66% effective rate vs Illinois: 1.92% of home value per year. Illinois's rate is 0.26 percentage points higher.
Sales tax: Connecticut: 6.35% combined state and average local rate vs Illinois: 8.98%. Illinois's combined rate is 2.63 percentage points higher.
Official Websites
Connecticut official website · Illinois official website
More Size Comparisons
All Connecticut 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.