Lake County is a county situated in the northeastern corner of the U.S. state of Illinois along the shores of Lake Michigan. According to the 2010 census, it has a population of 703,462, making it the third-most populous county in Illinois after nearby Cook and DuPage Counties. Its county seat is Waukegan, the ninth-largest city in Illinois. Lake County is one of the collar counties of the Chicago metropolitan area, located immediately to the north of Cook County.
According to the U.S. Census Bureau, the county has a total area of 1,368 square miles (3,540 km), of which 444 square miles (1,150 km) is land and 935 square miles (2,420 km) (67.6%) is water. It is the second-largest county in Illinois by total area and the only one that has more water area than land area. Most of the water is in Lake Michigan.
As of the 2010 Census, there were 703,462 people, 241,712 households, and 179,428 families residing in the county. The population density was 1,585.6 inhabitants per square mile (612.2/km). There were 260,310 housing units at an average density of 586.7 per square mile (226.5/km). The racial makeup of the county was 75.1% white, 7.0% black or African American, 6.3% Asian, 0.5% American Indian, 8.5% from other races, and 2.6% from two or more races. Those of Hispanic or Latino origin made up 19.9% of the population. In terms of ancestry, 20.5% were German, 12.9% were Irish, 9.4% were Polish, 6.9% were Italian, 6.5% were English, and 4.0% were American.
Of the 241,712 households, 40.8% had children under the age of 18 living with them, 59.6% were married couples living together, 10.4% had a female householder with no husband present, 25.8% were non-families, and 21.5% of all households were made up of individuals. The average household size was 2.82 and the average family size was 3.31. The median age was 36.7 years.
The median income for a household in the county was $78,948 and the median income for a family was $91,693. Males had a median income of $62,042 versus $44,200 for females. The per capita income for the county was $38,120. About 4.8% of families and 7.0% of the population were below the poverty line, including 9.6% of those under age 18 and 5.6% of those age 65 or over.