Meteorologists say a jet stream helped spread the smoke.
Officials are urging those who are sensitive to smoke to stay inside, drink plenty of water and limit outdoor exercise.
"The smoke is a big problem, added to the impact that mold count is higher, highest number we've had all year. The mold makes the smoke worse, and the smoke makes the mold worse," said Dr. Joseph Leija, Gottlieb Memorial Hospital.
The smoke caused some confusion before officials knew where the smoke was coming from.
"The majority of calls report a haze in the area and the smell of smoke in the area," Jen Wanek, Northwest Central Dispatch, said. "Probably received a couple of hundred calls altogether. At one point we were sending the fire department out until we learned later what was causing it."
The smoke is from the Pagami Creek forest fire near Ely, Minnesota. A lightning strike sparked the blaze on August 18, and it has spread to 60,000 acres in the Boundary Waters Canoe Area Wilderness, which is near the Minnesota-Canada border. Due to the dry conditions, the fire raced 16 miles east in a single day from Monday to Tuesday. More than 200 firefighters are involved in the effort to strike the fire.
A number of people in the northern and western suburbs called 911.
"We had three or four runs we made today that were false alarms," said Mayor Pete DiCianni, Elmhurst.
Ray West is visiting from Texas where they've been dealing with wildfires for weeks.
"I was hoping to come up here and have fresh air for a change. Instead, I got the familiar smell of smoke. It's a shame," he said.
Depending on the winds, the smoke remain in the area for the next couple of days.