CDC data shows Cook County is now among Illinois counties showing "substantial" community transmission of COVID-19.
DuPage, McHenry and Will counties were already at the "substantial" level. Joining those counties on Thursday are Cook, DeKalb, Grundy, Kendall LaSalle and Boone counties in Illinois.
In Indiana, Newton and Jasper counties are at "high" rates of transmission. Racine County in Wisconsin is at the "substantial" level.
As a result, the CDC recommends everyone in those counties start wearing masks indoors again, even if they're vaccinated.
DuPage County health officials said they strongly endorse the CDC guidelines.
CDC COVID-19 Transmission Levels by U.S. County Map not displaying correctly? Click here to open in a new window .
"The increase in activity we're experiencing is concerning given the high efficacy of the COVID-19 vaccine and our relatively high rates of vaccination in DuPage County. We continue to urge our residents who are 12 years and older to get vaccinated against COVID-19 as soon as possible to protect themselves and others against COVID-19 and the more dangerous Delta variant," said Karen Ayala, Executive Director of DuPage County Health Department. "COVID-19 vaccine providers are now widely available and likely within minutes of your home or workplace. Please visit www.vaccines.gov to find a location near you."
There is some encouraging data from DuPage County. More than 82 percent of residents 12 and older have received at least one dose of vaccine and 66-percent are fully vaccinated.