As of 2008, Illinois has an estimated population of 12,901,563, which is an increase of 75,754 from the prior year and an increase of 481,903 or 3.9%, since the year 2000. This includes a natural increase since the last census of 644,967 people; that is, 1,505,709 births minus 860,742 deaths and a decrease due to the net migration of 159,182 people out of the state. International immigration to the state resulted in an increase of 425,893 people and domestic migration produced a loss of 585,075 people.
As of the 2007 estimates from the U.S. Census Bureau, there were 1,768,518 foreign-born inhabitants of the state or 13.8% of the population, with 48.4% from Latin America, 24.6% from Asia, 22.8% from Europe, 2.9% from Africa, 1.2% from Northern America and 0.2% from Oceania. Of the foreign-born population, 43.7% were naturalized U.S. citizens and 56.3% were not U.S. citizens. Additionally, the racial distributions were as follows: 65.0% White American, 15.0% African American, 14.9% Latino American, 4.3% Asian American, 0.3% American Indian and Alaska Natives, and 0.1% Native Hawaiians and Pacific Islander American. In 2007, 6.9% of Illinois' population was reported as being under age 5, 24.9% under age 18 and 12.1% were age 65 and over. Females made up approximately 50.7% of the population.
According to the 2007 estimates, 21.1% of the population had German ancestry, 13.3% had Irish ancestry, 7.9% had Polish ancestry, 6.7% had English ancestry, 6.4% had Italian ancestry, 4.6% listed themselves as American, 2.4% had Swedish ancestry, 2.2% had French ancestry, other than Basque, 1.6% had Dutch ancestry, 1.4% had Norwegian ancestry and 1.3% had Scottish ancestry. Also, 21.8% of the population age 5 years and over reported speaking a language other than English, with 12.8% of the population speaking Spanish, 5.6% speaking other Indo-European languages, 2.5% speaking Asian and Austronesian languages, and 0.8% speaking other languages.
At the northern edge of the state on Lake Michigan lies Chicago, the nation's third largest city. In 2000, 23.3% of the population lived in the city of Chicago, 43.3% in Cook County and 65.6% in the counties of the Chicago metropolitan area: Will, DuPage, Kane, Lake and McHenry counties, as well as Cook County. The remaining population lives in the smaller cities and rural areas that dot the state's plains. As of 2000, the state's center of population was at 41°16′42″N 88°22′49″W / 41.278216°N 88.380238°W / 41.278216; -88.380238, located in Grundy County, northeast of the village of Mazon.
Catholics and Protestants are the largest religious groups in Illinois. Roman Catholics, who are heavily concentrated in and around Chicago, account for 30% of the population. Chicago and its suburbs are also home to a large and growing population of Hindus, Jews, Muslims, and Sikhs. The largest denominations by number of adherents in 2000 were the Roman Catholic Church with 3,874,933; the United Methodist Church with 365,182; and the Southern Baptist Convention with 305,838.
Because of its central location and its proximity to the Rust Belt and Grain Belt, Illinois is a national crossroads for air, auto, rail and truck traffic.
Chicago's O'Hare International Airport (ORD) is one of the busiest airports in the world, with 59.3 million domestic passengers annually, along with 11.4 million international passengers in 2008. It is a major hub for United Airlines and American Airlines, and a major airport expansion project is currently underway. Chicago Midway International Airport (MDW) is the secondary airport in the Chicago metropolitan area, serving 17.3 million domestic and international passengers in 2008.
Illinois has an extensive passenger and freight rail transportation network. Chicago is a national Amtrak hub and in-state passengers are served by Amtrak's Illinois Service, featuring the Chicago to Carbondale Illini and Saluki, the Chicago to Quincy Carl Sandburg and Illinois Zephyr, and the Chicago to St. Louis Lincoln Service. Currently there is trackwork on the Chicago-St. Louis line to bring the maximum speed up to 110 mph (180 km/h) which would reduce the trip time by an hour and a half. Nearly every North American railway meets at Chicago, making it one of the largest and most active rail hubs in the world. Extensive commuter rail is provided in the city proper and immediate northern suburbs by the Chicago Transit Authority's 'L' system. The largest suburban commuter rail system in the United States, operated by Metra, uses existing rail lines to provide direct commuter rail access for hundreds of suburbs to the city and beyond.
Major U.S. Interstate highways crossing the state include: I-24, I-39, I-55, I-57, I-64, I-70, I-72, I-74, I-80, I-88, I-90, and I-94. Illinois carries the distinction of having the most primary (2-digit) Interstates pass through it among the 50 states. In 2007, there were 1,248 traffic fatalities on Illinois roadways, the fewest since 1924.
In addition to the state's rail lines, the Mississippi River and Illinois River provide major transportation routes for the state's agricultural interests. Lake Michigan connects Illinois to all waterways east.
Chicago is the largest city in the state and the third most populous city in the United States, with its 2007 estimated population of 2,836,658. The U.S. Census Bureau currently lists seven other cities with populations of over 100,000 within Illinois. Based upon the Census Bureau's official 2007 scientific estimates, they are: Aurora, a Chicago outlier, which at 170,855 has recently (2006) eclipsed Rockford for the title of "Second City" of Illinois. However, at 156,596, Rockford is not only the number three city, but also remains the largest city in the state not located within the Chicago metropolitan area. Joliet, a large city located southwest of Chicago, is the fourth largest city in the state, with a population of 144,316. It is also one of the fastest growing cities in the U.S. Naperville, a suburb of Chicago, is fifth with 142,479, it shares its western border with the state's second largest city, Aurora, along Illinois Route 59. Springfield, the state capital of Illinois, comes in sixth with 117,090. Peoria, which decades ago was the second largest city in the state, comes in seventh with 113,546. The final city in the 100,000 club is Elgin, an outlying northwest suburb of Chicago with a 2007 estimated population of 104,288. Other major urban areas include the Illinois portion of Greater St. Louis (often called the Metro-East area), which has a population of over 691,000 people, the Illinois portion of the Quad Cities area, which has a population of 215,000, the Champaign-Urbana Metropolitan Area, which has a combined population of 210,000 and the Bloomington-Normal area with a combined population of over 125,000.