There are 153 US Post Offices in Cook County serving a total of 4,935,347 residents equating to 32,257 residents per post office. It's estimated that approximately 7,877,365 packages are handled across the 153 county post offices annually. Cook County is a county in the U.S. state of Illinois. It is the second-most populous county in the United States after Los Angeles County, California. As of 2014, the population was 5,246,456. Its county seat is Chicago, the largest city in Illinois and third-most populous city in the United States. More than 40% of all residents of Illinois live in Cook County. Cook County's population is larger than that of 29 individual U.S. states and the combined populations of the seven smallest states. There are 135 incorporated municipalities partially or wholly within Cook County, the largest of which is Chicago, which is home to approximately 54% of the population of the county. That part of the county which lies outside of the Chicago city limits is divided into 30 townships, which often divide or share governmental services with local municipalities. Geographically, the county is the fifth largest in Illinois by land area and shares the state's Lake Michigan shoreline with Lake County. Including its lake area, the county has a total area of 1,635 square miles (4,234.6 km2), the largest county in Illinois, of which 945 square miles (2,447.5 km2) is land and 690 square miles (1,787.1 km2) (42.16%) is water. Cook County's land is mainly urban and very densely populated. Cook County is included in the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area. It is surrounded by the five collar counties."