Lake County has been home to many military men and women over the years. In addition to those who have served from Lake County in the various branches of the service, Lake County once had two military bases which hosted soldiers and sailors from all over the country: Fort Sheridan and the Great Lakes Naval Base. Only Great Lakes Naval Base remains. Fort Sheridan was closed down. The cemetery, golf course, and some of the historic buildings still remain on the Fort Sheridan property.
A list of Lake County Illinois Pensioners can be found here. The list is not just made up of soldiers, but includes widows and parents, in some cases.
World War I Draft Registrations can be a valuable resource. Registrations for Lake County are available on microfilm in the collection of the Lake County IL Genealogical Society at Fremont Public Library in Mundelein.
Illinois in the Mexican War Database Records of the Services of Illinois Soldiers in the Black Hawk War, 1831-32, and in the Mexican War, 1846-8 by Isaac H. Elliot (pub. 1882). Compiled by volunteers for the Palo Alto Battlefield National Historical Park into this database. A database of almost 5,600 Illinois men who enlisted as volunteers for the Mexican War (1846-1848). The place of enlistment is listed by city, not county. The troops would organize and then travel to a designated city to be enlisted.