From: Juozas Rimas

> As for your Northern Illinois accent. Chicago? Northern Cities
Vowel Shift? Do you hear 'chopsticks' when someone not of your
dialect says 'ChapStix'  (ChapStix is the brand name of a lip balm).

I'd be grateful for a short explanation of what the Vowel Shift is
and where the Vowel Shift Belt is situated.

A useful URL
If you follow the links, especially to map 1, you see one version of how US dialects are divided. This map asserts there is a 'Western' dialect zone; other maps extend Midlands into the west. Within the understandings of this site, my dialect, then, becomes 'Western'.
As for the Northern Cities Vowel Shift, this page covers it rather fully in a section lower down.
My command of phonology is insufficient to give a clear description of what is happening. This is something I've only heard of, and not experienced personally.