The 2018 Oracle Challenger Series – Chicago was a professional tennis tournament played on outdoor hard courts.

This tournament was part of the 2018 ATP Challenger Tour and the 2018 WTA 125K series.

The first edition took place from September 4 to 9, 2018 in Chicago, United States.

The following players received wildcards into the singles main draw: The following players received entry into the singles main draw as alternates: The following players received entry from the qualifying draw: The following players received entry as lucky losers: The following players received wildcards into the singles main draw: The following players received entry from the qualifying draw: