Despite earlier reports that the gunman was killed, authorities say he is alive and is hospitalized in stable condition.
The gunman holds the rank of major and is a psychiatrist.
It is believed to be the country's deadliest mass shooting at a U.S. military base in history.
Fort Hood is near Killeen, Texas between Austin and Waco.
Investigators say Major Nidal Malik Hasan, 39, was the only shooter and he was armed with two handguns.
Texas senator Kay Bailey Hutchison says Hasan was about to deploy to Iraq and he was angry about that and she says Hasan was targeting people he knew.
Investigators say the shooting rampage started around 1:30 on Thursday afternoon when Major Nidal Malik Hasan opened fire inside the Soldier Readiness Center, a spot on base that was packed with soldiers getting clearance before deployment overseas.
Military officials say Hasan was shot following an exchange of gunfire with civilian police.
On Thursday night, there was praise for those who helped stop the gunman and those who helped the injured.
"God bless these soldiers and their quick reaction ripping uniforms apart, taking care of each other?it could have been much worse," said Lt. Gen. Robert Cone, Corps Commander, Fort Hood.
Hasan was just promoted to army major in May and has spent 25 years in the military. He had been practicing psychiatry at the Walter Reed Army Medical Center and was recently transferred to the Darnell Hospital at Fort Hood.
According to medical records, Hasan is licensed in Virginia and Maryland. He attended Damascus Univeristy in Syria and may have been a native of Jordan but was an American citizen and, according to a family member, was raised in the United States.
Investigators say the weapons used were not issued by military.
"He is not talking to the military right now," said Lt. Cone.
Fort Hood is the largest active duty armored post in the United States including nine schools.
An Internet message help spread the word, but for those off the post it was even more frightening.
Fort Hood is home to nearly 52,000 troops.
President Barack Obama called the shootings a "horrific outburst of violence."
"It's difficult enough when we lose these brave Americans in battle overseas. It's horrifying that they should come under fire at army base on American soil," said Obama.
Investigators say Hasan had come to their attention at least six months ago because of internet postings that discussed suicide bombings and other threats.
Authorities will go to Hasan's home and get his computer, telephone records and look for connections to a possible broader conspiracy.
On Friday schools will be open and there will be a day of mourning at Fort Hood.