5 Most Populated Counties in the US

2. Cook County, Illinois

Population Estimates (2023): 5,087,072

Second on the list of most populated counties in the US, Cook County experienced a 3.6% population decline from 2020 to 2023, bringing the population count down to 5,087,072 from 5,275,555. By total area, Cook County spans across 944.9 sq. miles, and is the 6th largest county in the state of Illinois.

Moreover, a whopping 42.4% of the residents in Cook County have attained a bachelor’s degree or higher, which demonstrates the educational enthusiasm of the Cook County residents. If we look at the economy in the county, we see that it houses 134,715 employer establishments and 62.5% of the working residents are employed. Also, according to the Census data, the median household income in Cook County is only $76 lower than the median household income in Illinois, standing at $76,632 as of 2024.