The explosion happened about 9:30 p.m. Sunday at a house on Polaris Drive in far northwest suburban Lake in the Hills.
When firefighters arrived, they found flames going through the roof of a vacant townhome.
The flames spread to an occupied house next door, destroying both buildings. Other nearby homes also sustained smoke and water damage.
Fire officials praised neighbors for pounding on doors and making sure everyone in the townhomes got out safely.
One person was treated for smoke inhalation. More than a dozen people are now looking for a new place to live.