OK, Chicago lies right on the line dividing zone 8 and 9. Mine was set at 8 from the dealer.

Also did everyone with a NAV set the Timezone and DST correctly?
Mine was not set by the dealer.
Having it set correctly enables using the "Arrival Time" mode instead of the "Time to Destination". I'd rather know the actual time of day I'll arrive rather than hours and minutes to the destination. But that's me. And it's easy to change with a single button push even when in motion.
My '04 Prius did not have this option.
J