Police say the assault rifle attack in the Los Angeles suburb of Azusa wasn't election-related.
The two polling sites were shut down for several hours on Tuesday while officers surrounded a home where the gunman's body was found. One later reopened.
Authorities called to the scene got into a gun battle and police say it's unclear whether they fatally wounded the gunman or he killed himself. No officers were hurt.
The shooting took place not far from several schools, including one that was serving as a polling place, and across the street from a park that also had a polling site.
Police don't have a specific motive for the shootings.
The names of the gunman and the dead man haven't been released. The wounded victims are described as two women in their mid-50s.
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Azusa police had advised residents to stay clear of the area and shelter in place as officers combed the neighborhood for at least one suspect believed to be heavily armed.
Local government official Dean Logan advised voters to find other polling sites to cast their ballots.
"Voters should avoid the area and, if necessary, cast a ballot at an alternate polling location," he tweeted.
A woman inside one of the affected polling stations said she heard shots ring out before officials placed the area on lockdown. Some 30 people were inside when the incident unfolded, she said.
"At first, I thought it was construction but people came running into the room saying they see a guy with a bulletproof vest and a white shirt," she told CNN. "As of right now, they just have us in the voting room and are trying to keep us calm."
