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, and its Chicago Portage area preserve is also affiliated with the United States National Park Service.