Thin-crust (or "tavern style" as some call it) has been widespread across the city for quite awhile.
> As of 2013, according to Grubhub data and the company Chicago Pizza Tours, thin-crust outsells the more widely known deep-dish style among locals, with GrubHub stating that deep-dish comprises only 9% of its pizza deliveries.
https://en.wikipedia.org/wiki/Chicago-style_pizza#Thin-crust...