Pro-Tip, Vote Early!

Once you have voted the calls will nearly stop.
The parties keep track of who has voted, they concentrate their efforts on those who have NOT voted yet.
Some campaigns are not as good at tracking voters and may still call but they will stop too if you tell them you already voted.
I'm off to stand in line and get it done ASAP.
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Voted, first in line, first early vote cast at my polling location.

How do they track who has voted? I have never heard anyone having access to the system.

Same way they have done it for decades.
County registrar of voters keeps a tally of who has voted.
Poll watchers copy the list a few times a day and give it to runners who take it to local party headquarters where it is compared to the master voter rolls.
Made easier by the precinct structure.
The most serious use of this is on election day but it will be done for early voting if enough volunteers are available.

In honest elections this also helps to prevent vote fraud, in Chicago not so much.