The Forest Preserve District of Cook County is a governmental commission in Cook County, Illinois, that owns and manages land containing forest, prairie, wetland, streams, and lakes. These land holdings are primarily managed as undeveloped natural areas and for outdoor recreation. The Forest Preserve District encompasses approximately 70,000 acres of land or approximately 11% of the land in Cook County, which contains the city of Chicago and is the most densely populated urban metropolitan area in the Midwest. The Forest Preserves also owns the lands on which the Brookfield Zoo and the Chicago Botanic Garden operate.

Cook County is the most populous county in the U.S. state of Illinois and the second-most-populous county in the United States, after Los Angeles County, California. More than 40 percent of all residents of Illinois live within Cook County. As of 2020, the population was 5,275,541. The county seat is Chicago, the most populous city in Illinois and the third most populous city in the United States. The county is at the center of the Chicago metropolitan area.