Poffenberger, 62, is two years past the state's mandatory retirement age.
State officials said the federal Age Discrimination Act prevented Maryland from retiring Poffenberger when he reached 60. But that law was amended last July, officials said.
Sgt. Laura Lu Herman, a state police spokeswoman, said officials waited until this month to inform Poffenberger because they wanted to explore possible alternatives. But she said the law makes an exception only for the state police superintendent.
"We have bent over backwards trying to help him," Herman said. "We tried to see if there was anything we could do to keep him on. There are no exceptions. There's no way around it."
Herman said state police officials have discussed other options with Poffenberger. For instance, she said he could serve the force as a civilian in some capacity.
"It's frustrating for us because he's a great trooper," she said. "We hate to lose somebody who's dedicated his entire life to the Maryland State Police."
Poffenberger said he feels disappointed because his age, not his qualifications, is preventing him from reaching the 40-year plateau. He said he recently returned from the shooting range with an expert rating and passed his last physical exam.
"Everything's tops . . . except the age thing," he said.
The mandatory retirement sparked shock and outrage among some Washington County residents who have come to know him well over the years.
Boonsboro Mayor Charles F. "Skip" Kauffman Jr. earlier this month presented Poffenberger with the keys to the town to honor him for his years of service. Poffenberger spent several years patrolling the southeast part of the county.
Kauffman recalled a time when town officials discovered the town community center had been burglarized. He said Poffenberger surveyed the situation, left, and then returned a short while later with a youth who admitted to the break-in.
It was just one example of Poffenberger's quick thinking, Kauffman said.
"I think it's a great loss for the town of Boonsboro and Washington County," Kauffman said. "Trooper Poffenberger served well for 37 years," he said. "I can't understand why they would make a competent person like that retire. He was one of the better ones."
Poffenberger, whose son is also a Maryland State Police trooper, said last month that he always wanted to be a state trooper - even when he worked as a commercial illustrator.
Poffenberger said he has not given any thought about what he will do in retirement. As for the job, he said he will plug away as he has for the last 37 years.
"Just keep working, I guess - until it's over," he said.