That's according to Bruce Parry, who decades ago, was among them. Now, he is with the Illinois Union for the Homeless.
"It was a direct result of PTSD. I was homeless for several months," Parry said.
As an Army infantry platoon leader and a company commander who saw a lot of combat, Parry served 20 months in Vietnam, but it was 20 years later when he hit rock bottom and sought help. He now devotes his life to helping unhoused veterans.
Parry said there are a variety of reasons why vets experience homelessness.
"Veterans, particularly enlisted veterans, are poor. They don't make enough money to be out of poverty," Parry said.
Parry says the transition from military to civilian life can be difficult.
"Every VA has a homeless department, and my experience with that is it insufficiently resourced for a very pervasive problem," Parry said.
To address homelessness within the veteran community, Illinois U.S. Rep. Delia Ramirez plans to introduce legislation soon. She says the number of unhoused veterans has increased by 7% during the past year.
"The legislation itself will specifically add additional comprehensive support services to be able to move people into permanent housing as quickly as possible, as well as increase the funding for the housing providers," Ramirez said.
Ramirez is hoping to get bipartisan support.
"The idea that a veteran who has served this nation and nearly died for this country is experiencing homelessness is unacceptable," Ramirez said.
But Ramirez admits her proposed legislation will be an uphill battle. She said last year, Republicans slashed the Veteran Affairs Budget and this year, they are talking about doing it again by at least 15%.