With an investigation still underway, it appeared that seven people were shot and killed in four different residences in the small town of Tyrone.
An eighth person, described as an elderly woman, was found dead in a fifth house, apparently "from natural causes," the Missouri State Highway Patrol said.
Her relationship with the gunman and the victims was not immediately disclosed.
"The apparent suspect, a 36-year-old male from Tyrone, was found dead in a vehicle... In (neighbouring) Shannon County from an apparent self-inflicted gunshot wound," added police spokesman Sergeant Jeff Kinder.
No names were released pending notification of next of kin.