"The sheriff's department can confirm the apparent death by a self-inflicted gunshot wound of Hunter S. Thompson at his home," Tricia Louthis, a spokeswoman for Colorado's Pitkin County government, told AFP.
Authorities declined to give any further details on Thompson's death. But son Juan Thompson, who reportedly found the author's body at his home, near the ski resort of Aspen, about 256 kilometres (160 miles) south-west of Denver, issued a statement.
"On February 20, Dr Hunter S. Thompson took his life with a gunshot to the head at his fortified compound in Woody Creek, Colorado," the statement, released to the Aspen Daily News, said.
Appealing for privacy for the family, he said arrangements for a memorial service would be made public soon.
Born in July 1937, Thompson was known for his explosive and comically cutting writing style with which he spun outlandish tales to describe his experiences. He was considered one of the most important American authors of the 20th century.
The ever-rebellious Thompson was born in the southern state of Kentucky and frequently got into trouble with the law in his early years for drinking and vandalism.
He joined the US Air Force in 1956 and studied journalism at New York's Columbia University. Thompson is survived by his second wife, Anita Beymunk, whom he married two years ago, his son Juan and a grandson.