The woman complained that a man at Caldwell Woods was questioning her citizenship and telling her she shouldn't be wearing the shirt.
Puerto Rico is a U.S. commonwealth. A video of the June 14 incident has since gone viral and shows the officer on scene did not respond.
Later, more officers arrived and arrested the man, who was described as drunk.
Caldwell Woods is part of the Forest Preserves of Cook County. The agency tweeted Monday that an investigation of the officer is ongoing. It says all visitors should feel safe.
We are aware of the the June 14 incident and video. After the incident, we immediately launched an investigation pursuant to our personnel policies into the response of our officer.— Forest Preserves (@FPDCC) July 9, 2018
All people are welcome in the Forest Preserves of Cook County and no one should feel unsafe while visiting our preserves.— Forest Preserves (@FPDCC) July 9, 2018
The investigation is ongoing and the officer involved has been assigned to desk duty pending the outcome. The intoxicated individual involved in the incident was arrested and charged with assault and disorderly conduct.— Forest Preserves (@FPDCC) July 9, 2018
Ricardo Rossello, the governor of Puerto Rico, wants the officer fired.