With the 773 area code in Chicago, many numbers have changed, but all Police Department phone numbers (which have the prefixes 744,745, 746, and 747) still retain the 312 area code, regardless of where the police facilities are located.
Simply put, this means that if you live in an area which falls under the 773 area code and would like to contact your district station or other Police Department unit, you must dial the 312 area code.
And please remember when reporting any non-emergency situations, do not go through 9-1-1. instead, dial 3-1-1.