Authorities apprehended the shooter before noon local time.
Parts of Fort Stewart went into a lockdown about an hour earlier.
All soldiers were treated on-site and moved to Winn Army Community Hospital for further treatment, the military base said in a Facebook post.
"There is no active threat to the community," the post said.
The incident remains under investigation.
Earlier on Wednesday morning, all personnel in the locked-down area had been urged to "stay inside, close and lock all windows and doors".
Located about 64 kilometres southwest of Savannah, Fort Stewart is the largest US Army post east of the Mississippi River.
It's home to thousands of soldiers assigned to the Army's 3rd Infantry Division and family members.
The fort's three elementary schools were also on lockdown, Community Superintendent Brian Perry told WTOC-TV.
The schools have nearly 1400 students, according to the Department of Defence.
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