The individual was in contact with the first case, which was reported on Aug. 24 and connected to Kaneland High School.
The Kane County Health Department is investigating the second case. The individual is vaccinated against the measles, officials said.
The vaccination provides strong protection against measles, mumps and rubella, health officials said.
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Health officials say anyone vaccinated and potentially exposed should monitor themselves for 21 days after exposure for symptoms. Symptoms include high fever, cough and rash.
Individuals exposed and unvaccinated should follow quarantine restrictions.
If you develop symptoms, call your healthcare provider before going to a medical facility. Do not go to an emergency department or other healthcare facility without calling ahead.
The first confirmed case was the first measles case reported in Kane County since 2019. Before that, the county had not recorded a case since the 1990s.
Health officials said measles was declared eliminated in the United States in 2000, but the number of cases has increased significantly across the country. They warned that the nation is now in danger of losing that eliminated status.