The four victims — two juveniles and two adults — were taken by ambulance to a hospital, where the teen, who was shot in the chest, died, authorities said.
The sheriff's office provides policing services under a contract with Windsor. Sheriff Steve Freitas did not respond to several messages Sunday seeking comment.
Windsor police said a suspect in the shooting fled in a blue Nissan compact. They described him as a black man wearing a black shirt and sweatpants.
The vehicle, driven by a female and possibly holding two other passengers, was last seen eastbound on Windsor River Road.
Focha on Sunday said she could not provide additional details about the suspect or whether additional people were being sought.
Focha also declined to elaborate on her statement that it was "unknown if the violence was gang-related."
Investigators worked Sunday morning behind yellow police tape which cordoned off the 500 block of Windsor Ave, just north of Windsor River Road.
Two pickups, also behind yellow tape, were parked in the driveway of the gray-green split-level house at the corner of Windsor River Road and Windsor Avenue.
"That's a damn shame," said Al Stoller, the next-door neighbor, when told of the fatality.
Stoller, who said he vaguely knows the residents, said he heard music from an apparent party starting up Saturday afternoon, describing it as "nothing obnoxious."