It could have begun in the 1940's with a restaurant in Columbus, OH run by Teresa Marzetti. She named a dish much like chili mac after her brother-in-law, Johnny Marzetti. Most of us grew up eating various versions of Johnny Marzetti. Another possible source is that it originated in Cincinnati, OH and is associated with the Cincinnati Chili franchise. Cincinnati chili is pasta covered in chili, so it's not exactly chili mac. No matter where it came from, it's definitely a recipe that should be added to your rotation.