Cook County Government | 41,511 followers on LinkedIn. As the largest county in the state and the second largest in the nation, Cook County is a hub for residents and business | Welcome to Cook County, IL, the second-most populous county in America with more than 5 million residents. We have long been a global beacon of opportunity and progress, driving ways to grow with our diverse residents, businesses, organizations, and universities. Led by Cook County Board President Toni Preckwinkle, we take pride in running an open, honest, and efficient government that provides high-quality services to our dynamic center for culture, industry, and travel.