Map - Lake County, Illinois (Lake County)

Lake County is situated in the northeastern corner of the U.S. state of Illinois, along the shores of Lake Michigan. As of the 2020 census, it has a population of 714,342, making it the third-most populous county in Illinois. Its county seat is Waukegan, the tenth-largest city in Illinois. The county is primarily suburban, with some urban areas and some rural areas. Due to its location, immediately north of Cook County, Lake County is one of the collar counties of the Chicago metropolitan area. Its northern boundary is the Wisconsin state line.

According to the 2010 census, Lake County is the second wealthiest county in the state by per capita income, after DuPage County. Additionally, Lake County ranks as the 27th wealthiest county in the nation. The county includes the affluent North Shore communities of Lake Forest, Lake Bluff, and Highland Park, and much of the county's wealth is concentrated in this area, as well as in communities bordering Cook County to the south and McHenry County to the west. The north and northwest areas of the county, though historically rural and exurban, have experienced rapid suburbanization in the past three decades, while the lakefront communities of Waukegan, North Chicago, and Zion are post-industrial areas and majority non-white.

Naval Station Great Lakes is located in the city of North Chicago. It is the United States Navy's Headquarters Command for training, and the Navy's only recruit training center.

The county, which was primarily unsettled prairie and was still home to its native Potawatomi Indians, was created by the Illinois State Legislature in 1839. At that time, Libertyville, then known as Independence Grove, was the first county seat. In 1841, however, the county's residents voted to move the county government to Little Fort, now Waukegan, where the commissioners had purchased a section of land from the state. Lake County's first courthouse was built on part of that land in 1844 and the remainder was sold to pay for the $4,000 construction cost.

The county's first courthouse was used solely for court sessions and the jail, but in 1853, commissioners constructed a building to accommodate county administration offices and house records. When fire damaged the courthouse on October 19, 1875, the county records were saved because they were in the adjacent building.

After the fire, proposals were made to move the county seat to Highland Park, Libertyville or another site in central Lake County. The county commissioners, however, decided to rebuild in Waukegan. The east half of the building was reconstructed at a cost of $45,000. In 1895, the first jail building was added to the government complex and a west addition was added to the courthouse in 1922. By 1938, county commissioners saw a need for additional space and approved the addition of a 5th Floor. This courthouse, however, was demolished in 1967 to make room for a new high-rise administration building, which was completed with the addition of the jail in 1969 and courts in 1970.

Shortly thereafter, the Lake County Board commissioned the construction of a multi-faceted justice facility and ground was broken in 1986 for the Robert H. Babcox Justice Center, named in memory of Sheriff Babcox, who served as Lake County Sheriff from 1982 to 1988. The justice center, which houses the county jail, work release program, sheriff's administration offices and three courtrooms, was finished in 1989 at a cost of $29.6 million.

Additional county government facilities have been built or expanded throughout Lake County, including the Coroner's Office, Health Department/Community Health Center facilities, Division of Transportation, Public Works and Winchester House. Lake County government services extend throughout the county's 470 sqmi.

The historic Half Day Inn, a tavern/restaurant, was constructed in 1843. This structure, once located at the corner of Milwaukee Avenue and Rte. 45/Old Half Day Road, was one of the oldest structures in Lake County until it was demolished in 2007 to make way for retail space, condominiums, and a retention pond.