This time, though, his office will be going it alone.
Arizona Attorney General Mark Brnovich has chosen to side with Arizona voters.
On Tuesday, Montgomery filed a petition to the Arizona Supreme Court in White Mountain Health Center v. Maricopa County, keeping up a fight he began in 2011.
Former AG Tom Horne, who lost to Brnovich in the 2014 Republican primary election, helped Montgomery by filing with the county as an intervenor and additional defendant in the case.
Things haven't gone well for the prohibitionists. In December, the Arizona Court of Appeals ruled 3-0 against Maricopa County and the state.
The ruling made Brnovich's office partially responsible for a $200,000-plus debt of attorneys' fees.
Now, as the petition shows, Brnovich is not joining with Montgomery in the new appeal to the state Supreme Court.
"The attorney general's office is not participating in the appeal," the AG's office spokesman, Ryan Anderson, wrote in an e-mailed response to Phoenix New Times' questions. "All inquiries regarding the lawsuit should be directed to the county attorney's office."
The AG's office can't escape the attorneys' fees already levied against the state and county in the case. But if Montgomery's side loses again, county taxpayers will have to shell out more money for lawyers' fees and, potentially, for awards or sanctions.
Montgomery didn't return a message seeking comment for this article.
The two elected officials clearly don't see eye to eye on cannabis.
Both are high-achieving lawyers and Republicans.
But Montgomery's a West Point graduate and former Army tank commander; Brnovich has an undergraduate degree from Arizona State University and is an unapologetic fan of the Grateful Dead.
Brnovich told New Times in 2015 that he had never tried marijuana or any other illegal drug, but he supports the decision of voters.
He said back then that he will "defend what the voters do," and that the attorney general had "an obligation to defend that."
Another theory for why Brnovich isn't following in Horne's footsteps: The case has been a loser for the government.
It began in 2011, a year after voters narrowly approved the Arizona Medical Marijuana Act (AMMA). While cities, towns, and counties around the state prepared to receive the retail medical-cannabis shops authorized by the law, Montgomery took a different tack.
He advised the county Board of Supervisors not to approve zoning for any dispensaries because, according to him, they would violate federal law. The board, including former Democratic Supervisor Mary Rose Wilcox, went along with his plan.
Entrepreneur and bong-tool inventor Daryl "Butch" Williams then sued the county when he was stymied from putting a dispensary in Sun City, a retirement community on unincorporated county land. He'd won the right to put a dispensary there in a lottery for the licenses held by the state Department of Health Services.
Local lawyer Jeff Kaufman and attorneys from the American Civil Liberties Union took the side of the dispensary.
Montgomery and Horne were shot down at every step.
Maricopa County Superior Court Judge Michael Gordon rejected their theories. He ruled that Montgomery was making a "transparent attempt" to stymie the law and sanctioned the county $5,000.
Montgomery tried to make an emergency appeal to the Arizona Supreme Court. It turned him down.
Williams opened his White Mountain Health Center dispensary in December 2014.
Montgomery didn't give up, and pressed his case with the Arizona Court of Appeals.
This past December, the appeals court reversed the sanction against the county, but otherwise ruled in favor of White Mountain.
The voter-approved law did not violate federal law, the court reaffirmed.
The appeals court also left in place more than $200,000 in White Mountain's legal fees that the county and state must pay "jointly and severally." That means both entities are equally responsible for the debt.
Part of the appeals-court decision was based on an April 2015 Arizona Supreme Court ruling that people on probation can't be banned generally from the medical-marijuana program. The 5-0 decision in that case, Reed v. Kaliher, backed up the idea that the AMMA did not conflict with federal law.
Quoting from a Michigan case, the judges ruled that "the people of Arizona 'chose to part ways with Congress only regarding the scope of acceptable medical use of marijuana.'"
Montgomery's claims in his new petition, which challenges the rulings in both the White Mountain and Reed v. Kaliher cases, are similar to those that the court has already found unconvincing.
That could simply mean more justices ruling against the county attorney this time.
But the petition gives hope to Montgomery and others who want to see patients arrested, thrown in jail, and charged under Arizona's felony prohibition laws.
The petitition (see below) was written by deputy county attorneys Bruce White and Joseph Vigil. It captures the flavor of Montgomery's personal jihad against legalized marijuana.
The argument boils down to the idea that the county has the right to enact reasonable zoning regulations. One of its criteria is that dispensaries must comply with both federal and state law.
"The Federal Controlled Substances Act ('CSA') expressly prohibits growing, distributing, and possessing marijuana in any capacity, other than as part of a federally authorized research program," the petition states. "It is a crime to violate it, regardless of state laws that purport to evade it. Despite the wishes of its promoters and the voters, the AMMA cannot change marijuana's classification as a federally prohibited Schedule 1 drug under the CSA."
The county wants to prohibit dispensaries because they violate federal law, according to new petition.
The state Supreme Court made a mistake, the petition states, in concluding that the law "did not represent an obstacle to enforcement of the CSA, but rather enhanced it in some unexplained fashion."
They claim, "there could be no more patent obstacle" and "no more blatant conflict" to the goals of federal law than state-legal cannabis retail and cultivation operations.
A January ruling by the Colorado Supreme Court agreed that voter-approved legalization laws conflict with the CSA, and therefore police can't return seized weed to people, the petition states.
As he's done previously, Montgomery tries to argue through the petition that state employees might be prosecuted under the CSA simply for running the voter-approved program.
No state employee in any state has been charged by the feds for helping to run a state-legal recreational- or medical-marijuana program.
The situation could change under the new president's administration, the petition states.
However, public comments on Thursday from Trump's spokesman, Sean Spicer, suggested that while the feds might take action against recreational-marijuana laws like those in Colorado or California, medical-marijuana programs like Arizona's could be safe. The head of a local dispensary association said he was "thrilled" with Spicer's apparent blessing of medical marijuana.
Steve White, one of White Mountain's lawyers, said he is confident the state Supreme Court will "reach the right decision" and not rule that federal law pre-empts the AMMA.
White said he's not surprised by Montgomery's dogged pursuit of the case.
"He has sworn that he will fight this pre-emption fight until he's told he can't do it anymore," White said. "So he's just fulfilling that promise. Economics don't seem to come into play."
Economics seem to matter to the state Attorney General, though — and so does the will of voters.