But how does it spread? Like a virus? Or is this more like a divine intervention that has a portion of the population all over the world simultaneously turning into zombies and spreading the disease? In your scenario, is Chicago Ground zero?
In Romero movies it is never explained.
If we want to be practical... it is some form of infection, obviously.
If all hell breaks loose it would either have to be an attack of some kind (bioweapon) or the dam breaks so-to-speak wherever you are.
I always envision the zombie apocalypse taking weeks or even months to take shape... more and more incidents would happen and the govt would try to contain it and cover it up.
Then one day something goes wrong... hospital is overrun... it starts spreading from there and snowballs because the govt can't contain it and local LEOs have no clue what they should be doing to contain it.
Suddenly you have streets filled with zombies, bitten people, and panic.
Maybe it is just one city at first and they try to contain that city.... then it happens in another city or town.... cracks in the dam... resources spread too thin.
In the scenario I imagine you are in a city or town (I presume most of us live in cities/towns) and in that area shit goes cray... how it goes for you would depend heavily on whether your city/town is one of the first cracks in the dam or one of the last...