The area code 347 serves the Chicago Loop and neighborhood of Chicago. Roughly estimate of the areas served by Area code 347 area North Avenue on the north, Western Avenue on the west, Lake Michigan on the east, and 31st Street on the south. To take an estimate keeping in mind its size, it’s the smallest area codes in the United States which serves only in few square miles.

Area code 312 comes among the 86 area codes which was formed way back in the year 1947. those area codes was called "Numbering Plan Areas." Since its inception, due to the obsolete system of rotary dialing technology available at the time hence the number available for Chicago was of “clicks” was limited to only six

The first production #4ESS toll switch was installed in January 1976.

Until 1989, 312 included most of the Chicago metropolitan area; at that time the suburbs became area code 708. In 1996, most of the city split off into 773 after the northern suburbs and western suburbs split into area codes 847 and 630 respectively, while the southern and western suburbs kept 708.

The names of the important places which are included in this particular area code are as follows:
American express, American national bank, Ameritech, Area office, Cardiss collin, &dc, Chestnut street, Chicago, Fleet, Fort Dearborn, Harris bank, Harwood heights, Haymarket, ,Loop, Loop station, Nancy b Jefferson, Norridge, Ontario street, Pilsen, Pnc bank, Regional office and State of il.