Deputies said more than 6,500 plants were seized from a field in rural Dayton with the help of SWAT officers and Drug Enforcement Administration agents. The crops are valued at more than $9 million.
Marijuana is legal and regulated in Oregon but law enforcement officers say illegal grow operations are still a big problem.
And a legal pot business owner in Yamhill County told KATU he predicts more illegal weed busts in the future, although perhaps not as large as the one on Tuesday.
Deputies said the illegal grow operation was part of a Mexican drug trafficking organization.
They said they located a man named Manuel Madrigal within the pot garden and took him into custody. Investigators said he comes from San Antonio, Texas and has a history of previous drug arrests.
"There is still a profit to be made in marijuana by these illegal organizations," Yamhill County Sheriff Tim Svenson said in a news release. "As long as this continues we will need to remain diligent in our investigations to keep this money from being routed to other areas of criminal activity."
"This goes against everything I've advocated for around here," Jim Galba, owner of the Medicine Tree marijuana dispensary in nearby McMinnville, told KATU on Wednesday.
He said he's shocked by the bust.
"I knew things like that still happened," Galba said, "but I had no idea a 6,500 plant illegal grow was happening in Yamhill County."
Galba said business is great even with five other legal dispensaries in town. And he said consumers should feel better buying weed like his legally.
"Everything has to go through a(n) Oregon certified lab," Galba said, "and tested for potency and the mildew and mold to ensure its quality."
But Galba also said regulations are very complicated in the legal pot business and federal taxes are a nightmare.
As this IRS document KATU found on the agency's website says, legal marijuana businesses can't write off many of the same expenses as other businesses.
"Everybody that works in here I can't deduct," Galba said while standing in his store. "The health insurance I provide for them I can't deduct ... my gloves, the electricity, the rent, advertising -- none of it."
He estimates he pays 60 to 70 percent in federal taxes.
Madrigal, meanwhile, appeared in federal court Wednesday.
A spokeswoman for the U.S. Attorney's Office in Portland said the case is still under investigation.