Buffalo Grove firefighters responded to the 300-block of Le Parc Circle just before 12:30 p.m.
The fire started in one townhome and spread to five others.
All the homes are now uninhabitable, and the damage is estimated at nearly $1 million.
One firefighter suffered a minor injury.
No residents were at home at the time of the fire. Firefighters found two cats, who were rescued.
The cause of the fire is under investigation.