Waukegan () is the largest city in and the county seat of Lake County, Illinois, United States. Situated approximately 35 miles (56 km) north of Downtown Chicago and 23 miles (37 km) northeast of O'Hare International Airport, it is a principal city within the Chicago metropolitan area. As of the 2010 census, the population of Waukegan was 89,078 (estimated to have declined to 86,075 in 2019), making it the ninth most populous city in Illinois. Waukegan is a predominantly working-class community, with a sizeable middle-class population.
The site of present-day Waukegan was recorded as Rivière du Vieux Fort ("Old Fort River") and Wakaygagh on a 1778 map by Thomas Hutchins. By the 1820s, the French name had become "Small Fort River" in English, and the settlement was known as "Little Fort". The name "Waukegance" and then "Waukegan" (meaning "little fort"; cf. Potawatomi wakaigin "fort" or "fortress") was created by John H. Kinzie and Solomon Juneau, and the new name was adopted on March 31, 1849.
Waukegan had an abolitionist community dating to these early days. In 1853, residents commemorated the anniversary of emancipation of slaves in the British Empire with a meeting. Waukegan arguably has the distinction of being the only place where Abraham Lincoln failed to finish a speech; when he campaigned in the town in 1860, a fire alarm rang, and the man soon-to-be president had his words interrupted.
During the middle of the 19th century, Waukegan was becoming an important industrial hub.