The family told the Associated Press on Monday that Sobol died in Miami on July 11.
"Thanks to Donald, generations of children have learned to read and solve mysteries alongside Encyclopedia Brown, one of the most iconic characters in children's literature," said Don Weisberg, president of Penguin Young Readers Group, which publishes Sobol's books.
The series featured amateur sleuth Leroy "Encyclopedia" Brown, who unraveled local mysteries with the help of his encyclopedic knowledge of facts great and small. The books were first published in the early 1960s.
The "Encyclopedia Brown" series were translated into 12 languages and has sold millions of copies worldwide. Sobol's latest Encyclopedia Brown adventure, "Encyclopedia Brown and the Case of the Soccer Scheme," will be published in October, according to a release from Penguin.
Next year marks the 50th anniversary of the "Encyclopedia Brown" series.
Sobol served in the Army Corps of Engineers during WWII and graduated from Oberlin College. He later worked as a copywriter at the New York Sun, where he eventually worked his way up to reporter. His first Encyclopedia Brown book was rejected two dozen times before it was published, his son said.
Sobol went on to author more than 80 books and wrote on a daily basis to the very end.
The Associated Press contributed to this report.