Five of the victims are men, one is a woman. Police said Sunday that the deaths are being investigated as homicides.
The victims had injuries that are suspected to have been caused by gunfire, Milwaukee Police Sgt. Efrain Cornejo said in an email to The Associated Press. The police department continues to seek "unknown suspects," he said.
Officers were called to the home for a welfare check just before 4 p.m. Sunday.
"At this time, the motive and information regarding any involved suspects is not known to us right now," said Assistant Chief Paul Formolo with the Milwaukee Police Department.
Formolo said the welfare check came from citizens who had concerns about the occupants of the house. He added that it is a normal call the department responds to all the time, but not usually with these results.
Autopsies are expected to take place Monday.
Investigators ask anyone with information to contact Crime Stoppers or the Milwaukee Police Department.
The Associated Press contributed to this report