Under the North American Numbering Plan (NANP) in United States of America, area code 630 along with the area code 331 covers mainly the western suburbs of the Chicago areas. The areas of DuPage County, Illinois are also covered by the telephone area code 630. Towards the northwest of Chicago area code 630 also serves the neighborhood of Cook County, which also includes the villages of Streamwood and Hanover Park. In the western area includes Kane County is divided between area codes 847 and 224 in the north, including Elgin, and area codes 630 and 331 in the south, including Aurora. To the south, the northern part of Will County and a small part of southern Cook County, including the village of Burr Ridge and parts of the village of Lemont, are also included in the 630 and 331 area codes. To the southwest, the city of Yorkville, in exurban Kendall County, is included, as well.

In the year 2007, area code 331 started overlaying 630 and ten-digit dialing was implemented in both the areas. Towards 1996, area code split off and 708 and in 1989, 708 was further splitted into area code 312.

The names of the places which are important in this particular region are as follows:
Addison, Argonne, Aurora, Bartlett, Batavia, Bensenville, Big rock, Bloomingdale, Bolingbrook, Boulder hill, Bradford group, Bristol, Burr ridge, Burr ridge il, Burr ridgex, Burridge, Carol stream, Citicorp, Clarendon hills, Cloverdale, Darien, Downers grove, Elburn, Electronic data systems, Elmhurst, Eola, Flowerfield, Fox valley, Fox valley facility, Geneva, Glen Ellyn, Glendale heights, Glendale hts, Great lakes area office, Hanover park, Hinsdale, Household finance corp, Household financial services, Inktel marketing, Itasca, Kaneville, Keeneyville, Lafox, Lemont, Lincolnwood, Lions international, Lisle, Little rock, Lombard, Medinah, Millbrook, Montgomery, Mooseheart, Naperville, North aurora, North suburban, Northern ill gas co, Northwoods, Oak brook, Oak brook mall branch, Oakbrook ter, Oakbrook terrace, Ontarioville, Oswego, Plano, Plattville, Rates and classification, Roselle, Saint charles, St charles, Streamwood, Sugar grove, Valley view, Villa park, Virgil, Warrenville, Wasco, Wayne, West Chicago, Westmont, Wheaton, Willow brk, Willow brook, Willowbrook, Winfield, Wood dale, Woodridge and Yorkville.