It happened in the 1300-block of Kennedy Street.
Three people were apparently standing in a front yard when someone threw a liquid chemical on them. The victims and their attacker are all related.
"They knew each other. It was a fight amongst themselves over-- I am not sure the exact topic, but I have a feeling once we get the precise topic we'll all agree it certainly was not something worthy of throwing Drano on somebody," said Sheriff Tom Dart, Cook County.
Four people are hospitalized with burns.
Sheriff Dart says charges may be filed in the attack.