St. John's was ranked in the USA Today Top 25 and Associated Press National Prep Poll each of Vetter's six years at the school. He had a 136-10 record at St. John's, and his 23-year mark is an astonishing 549-66 with three schools. His tenure ends with the Vikings on a 37-game winning streak.
"I am very proud of my years at St. John's," Vetter said in the release. "We established ourselves as one of the best programs in the country."
Vetter could not be reached for comment on Friday.
Vetter's longtime assistant, Kevin Sutton, is taking over as head coach at Montrose Christian in suburban Washington, and several players are expected to follow him.
Vetter's departure could also affect another Frederick County school. Levi Watkins, a freshman at Thomas Johnson, was set to transfer to St. John's, but it is now unclear where he will end up in the fall.
"I don't know where he's going to go," said TJ coach Tom Dickman. "I'm 99 percent sure he's not staying (at St. John's). I don't think he went there for anything other than to play basketball."
Dickman said he doubts Watkins will return to TJ.
"We'll still have kids at TJ to play," Dickman said. "Right now, I'm concerned with the kids that are there and want to play."