Erick M. Maya, 23, of the 5600 block of Park Avenue, Cicero, was charged with two counts of attempted murder, two counts of aggravated battery with a firearm and one count of unlawful use of a weapon by a felon.
The 33-year-old mother and her 15-year-old daughter were shot as they got into an SUV. Witnesses say a man walked up and fired several shots into the vehicle.
Romeoville police say that Maya and the 15-year-old victim had a previous dating relationship.
Romeoville police questioned four people Thursday but Friday morning, only Maya remained in custody.
One of the three people released had an outstanding warrant and was transferred to Will County Jail, police said.
It appeared to be a targeted attack, authorities said. Police have not released a motive.
"There was one shooter, and he was by himself. The other individuals, we're not sure what part they may have played in the incident," Chief Mark Turkey, Romeoville Police Department, said.
Police said the gunman opened fire as the woman and her daughter got into an SUV around 7 a.m. Thursday in the 300-block of Emery Avenue. Witnesses said a man fired two or three shots into the vehicle.
''I heard two gunshots, and I opened up my back door to look out, and I heard somebody screaming, and I ran out the front door and I saw her getting out of the driver's side, and she was holding her chest. So I ran over there, and she just had blood pouring out,'' said Brian Corban, the victim's neighbor.
Police say the suspect fled the scene on foot. Romeoville schools were on soft lockdown for several hours before being allowed back in the school around 10 a.m.
Neighbors say the family was new to the area. Both mother and daughter remain hospitalized in serious condition.