331 Area Code - Location, Time, Map, Cities and Census Data - ZIP-Codes.com
https://www.zip-codes.com/area-code/area-code-331.asp
WebArea Code 331 is located in Illinois. It covers 31 cities, including Aurora, Naperville, Bolingbrook, Wheaton, and Downers Grove. It also covers 5 counties, including Dupage County, Kane County, Kendall County, Cook County, and Will County. A full list of covered cities and counties is below including its prefix and population coverage.
DA: 71 PA: 59 MOZ Rank: 21