Aurora is a city in northeastern Illinois, United States. Located along the Fox River, it is the second-most populous city in Illinois, after Chicago, and the 144th-most populous city in the US. The population was 180,542 at the 2020 census. Aurora is the largest city in Illinois that is not the county seat of any county that it resides in. Founded within Kane County, Aurora's city limits have expanded into DuPage, Kendall, and Will counties.