The most populous cities in area code 331 are: Aurora, Naperville, Downers Grove, Saint Charles, and Elmhurst.
Other cities in the 331 area code include: Lombard, Lemont, Oswego, West Chicago, Wheaton, Bartlett, Sugar Grove, Geneva, Yorkville, Elburn, Warrenville, Oak Brook, Roselle, Bensenville, Plano, and Big Rock.
Aurora, a suburb of Chicago, is a city predominantly in Kane County and DuPage County, with portions extending into Kendall and Will counties. It is located in the outer region of Greater Chicago in the U.S. state of Illinois. It is the second most populous city in the state, and the 114th most populous city in the country. The population was 197,899 at the 2010 census, and was estimated to have increased to 199,963 by July 2013. Once a mid-sized manufacturing city, Aurora has grown tremendously since the 1960s. Founded within Kane County, Aurora's city limits and population have since expanded into DuPage, Will, and Kendall counties. Between 2000 and 2003, the U.S. Census Bureau ranked Aurora as the 34th fastest growing city in the United States. From 2000 to 2009, the U.S. Census Bureau ranked the city as the 46th fastest growing city with a population of over 100,000. In 1908, Aurora officially adopted the nickname "City of Lights", because it was one of the first cities in the United States to implement an all-electric street lighting system in 1881. Aurora's historic downtown is located on the Fox River, and centered on Stolp Island. The city is divided into three regions, The West Side, located on the west side of the Fox River, The East Side, located between the eastern bank of the Fox River and the Kane/DuPage County line, and the Far East Side/Fox Valley, which is from the County Line to the city's eastern border with Naperville.The Aurora area is home to an impressive collection of architecture, including structures by Frank Lloyd Wright, Ludwig Mies van der Rohe, Bruce Goff and George Grant Elmslie. The Hollywood Casino Aurora, a dockside gaming facility with 53,000 square feet (4,900 m 2) and 1,200 gaming positions, is located on the river in downtown Aurora. Aurora is also home to a large collection of Sears Catalog Homes (over 50 homes) and Lustron all-steel homes (seven homes).
Naperville is a city in DuPage and Will counties in the U.S. state of Illinois, and a suburb of Chicago. Naperville was voted the second-best place to live in the United States by Money magazine in 2006. It was rated 1st on the list of best cities for early retirement in 2013 by Kiplinger. In a 2010 study, Naperville was named the wealthiest city in the Midwest and eleventh in the nation with a population over 75,000. It was ranked among the nation's safest cities by USAToday and Business Insider. As of the 2010 census, the city had a population of 141,853, which was estimated to have increased to 147,100 by July 2015. It is the fifth-largest city in Illinois.
Downers Grove is a village in DuPage County, Illinois, United States. It was founded in 1832 by Pierce Downer, whose surname serves as the eponym for the village. Approximately 20 miles from the Loop, Downers Grove is a far south-western suburb of Chicago. The most recent census estimate tallied 49,715 residents in 2014.
The 331 area code lies within the Central Daylight Time Zone (or CDT). The current time in Central Daylight Time is 3:00 AM on Apr 01, 2023.