Perry Kucinich, 52, was found face down by another brother, Larry, at about 9 a.m., said Powell Caesar, a spokesman for the Cuyahoga County Coroner's office.
There were no signs of foul play, Caesar said. An autopsy was being performed Wednesday to determine the cause of death.
Larry Kucinich had taken his brother shopping Tuesday and then took him home but couldn't get an answer when he tried calling him Wednesday, Caesar said.
A statement from the congressman's office said Perry Kucinich was a artist whose works have been on display at a local art gallery. The statement said Perry and Dennis Kucinish were planning another showing of his works in the spring.
"He was an admirer of the works of Klee and Picasso, and the style and structure of his artwork derived from their influences," Dennis Kucinich said in a statement. "He was a genius. He had extraordinary insights. Although he struggled with mental illness, with the help of his family and friends, he was able to lead a productive life."
Dennis Kucinich took a flight from Washington to Cleveland after learning of the death, said his office press secretary, Natalie Laber.
"He was very close to Perry and he's taking this very hard," Laber said.
Kucinich, 61, is a six-term congressman from Ohio who is making his second bid for his party's nomination; he sought the nod in 2004. He registers in low single digits in polls and has raised little money for what is considered another long-shot run. Kucinich, who is known for his liberal views, has attracted a devoted following.
A Democratic rival, New Mexico Gov., offered his condolences to Kucinich and his family. "Barbara and I will keep your family in our thoughts and prayers," Richardson said in a statement.
Funeral services are pending, the congressman's office said. In addition to his brother Dennis, Perry is survived by brothers Frank, Gary, and Larry, and by sisters Theresa and Beth Ann.