A shooting inside a home killed six people, and a toddler was found in a nearby vehicle with a gunshot to the chest.
Police found the bodies while investigating a report of shots fired Saturday night in the small southern Wisconsin town, Chief Tim O'Neill said. Police interviewed friends and relatives of the victims Sunday morning, but released no details on the investigation or whether they had identified a suspect.
The wounded child, a 2-year-old girl, was listed in serious condition Sunday at the University of Wisconsin Hospital in Madison, O'Neill said.
O'Neill withheld the victims' names and declined to take questions at a brief news conference.
"We want to make sure there is no stone unturned," he said.
One of the victims was Vanessa Iverson, 19, who did not live at the house but had been visiting there, said her mother, Kay Macara, who went to the police station.
"My child," Macara said through tears. "I want answers."
In the house at the time of the shooting were a friend of Vanessa Iverson and the friend's husband, sister and brother-in-law, along with three children, including the 2-year-old and a set of twins, said Vanessa's sister-in-law, Sarah Iverson.
Marco Pastrana, 21, said his cousin, Ambrocio Analco, 22, was one of the dead. He said Analco went to the house early Saturday evening to drop off his twin boys, who were 2 or 3 months old, and 2-year-old daughter Jasmine.
The children's mother lived at the house, Pastrana said, adding that he did not know the twins' names or their mother's last name.
"I'm sad and mad at the same time because I don't know what happened," Pastrana said.
Police cordoned off a two-block area around the crime scene Sunday morning, wheeling out bodies as neighbors gathered on the sidewalks to watch the investigation on a tree-lined street just two blocks from the police station.
"It's tragic. It's getting worse all the time," said James Brandenburg, 57, who spent several minutes praying outside the house. "If we want to, we can put a stop to this."
The house where the shootings took place is a rental property where people often move in and out, said Pete Brancheau, 59, who lives across the street. He said he heard six shots Saturday night but thought nothing of it because children in the neighborhood play with firecrackers "all the time." About a minute later, he heard about three more shots.
"It's scary," Brancheau said. "Especially when there's a baby involved. There's no answer for it."
Tina McKinnon, 37, who lives down the street and around the corner, said she saw the family in the neighborhood but did not know them.
"It was a very quiet house," McKinnon said. "Never had any commotion whatsoever. The children were very pleasant."
Delavan is a bucolic community of 8,000 people about 40 miles (64 kilometers) southwest of Milwaukee. The two-block downtown area has brick-covered streets. The P.T. Barnum Circus, "The Greatest Show on Earth," was founded in Delavan in 1871.