Three people, including a police officer, were wounded and are in critical condition.
Investigators rushed to the nearby community of Cudahy, about six miles from the temple, where the gunman lived. Some homes in the area were evacuated.
Police are not saying much about the gunman or a possible motive.
Even after the gunman was killed, SWAT teams remained on the scene and spent hours going through the buildings. There were initially reports that there might have been multiple shooters involved.
Police now have determined that there was just the one gunman, it was simply a case of so many 911 calls coming in at one time, they were reporting seeing the same person from different perspectives as he made his way through the temple.
"Because of the heroic actions of our officers, they stopped this from being worse than it could've been," said Oak Creek Police Chief John Edwards.
It was bad enough. By the time it was all said and done, seven people were dead and three injured.
Among the dead, the gunman who, just after 10:30 Sunday morning walked into the Sikh Temple of Wisconsin and started shooting, moving from one part of the temple to another in search of victims.
Sot temple member "There were some priests who were in the living quarters," said temple member Harpreet Singh. "One of them got shot there."
There were several dozen people inside the temple at the time, getting ready for an 11:30 a.m. service.
Police say events came to a head when the first police officer arrived on the scene and began to tend to an injured person in the temple parking lot.
"When he engaged our officer, he ended up shooting him," Edwards said. "Another officer was on scene, he then engaged that officer by shooting at him. Our officer returned fire - killing the suspect."
Even as investigators remain at the temple Sunday night, combing the area for evidence and interviewing witnesses, the investigation has also moved six miles away to the neighboring community of Cudahy, to a duplex where it's believed the shooter lived.
"Any additional evidence, firearms, ammunition, any type of evidence from possibly his computer, any writings, manuscripts that he might have had, just something that would be another piece to the puzzle to determine exactly what made him do this," said Tom Ahem of the Bureau of Alcohol Tobacco and Firearms.
Those living in the nearby homes have been temporarily evacuated.
While it was earlier reported by local police that this was an act of domestic terrorism, in a statement Sunday night, the FBI says they have yet to make that determination.
Sikhism was founded in south Asia more than 500 years ago with roughly 27 million followers worldwide.
There are estimated to be about 500,000 Sikhs in the US, while the majority worldwide live in India.
Observant Sikhs do not cut their hair and male followers often cover their heads with turbans, which are considered sacred, and refrain from shaving their beards.
There is one Sikh temple in Chicago, in the Rogers Park neighborhood on the Far North Side.
Police say in light of the tragedy in Wisconsin, the district commander is giving the temple special attention.
"At this difficult time, the people of Oak Creek must know that the American people have them in our thoughts and prayers, and our hearts go out to the families and friends of those who were killed and wounded," President Barack Obama said in a statement. "As we mourn this loss which took place at a house of worship, we are reminded how much our country has been enriched by Sikhs, who are a part of our broader American family."
Victims memorial fund
C/o Sikh temple of Wisconsin
7512 S Howell ave
Oak creek Wisconsin
The Associated Press contributed to this report.