area code 312 is an area code that is part of illinois. it was one of the first area codes created in 1947. it initially covered the entire northeastern portion of illinois, but after it was split by 708 in 1989, 630, 847, and 773, all in 1996, it now covers only downtown chicago, with 708 and 773 covering the rest of chicago. it was overlaid by 872 in 2009.