Gov. Jon Huntsman Jr., who signed a proclamation commemorating the occasion, said Utah was participating in a role critical to national security.
"This is a milestone of which all of you should be proud," he said, noting that the depot's mission is for the "safe storage, surveillance and destruction" of the stockpile. "To that end, you have succeeded."
The million mark also moves Utah closer to reducing any and all risk for a leak of nerve agent outside the depot's boundaries, an incident Army officials say hasn't happened since the facility started destroying the weapons in 1996. One depot worker was exposed to a nerve agent, but is now back to work without any apparent long-term damage.
Col. Raymond Van Pelt, the depot's commanding officer, said all nerve agents will be destroyed at the facility by next year, with most destroyed by this June, leaving only mustard blister agents to be incinerated after that.
That's a stark change from the original tally of nearly 1.2 million munitions, or 13,617 tons of chemical weapons, held at the site before the destruction program began. Weapons have been stored at the depot since the early 1940s and some of the still existing munitions date to World War II.
The depot, 45 miles southwest of Salt Lake City, stores the aging weapons in "igloo" bunkers. The weapons are destroyed in a complicated process that includes heating the drained chemical agent to more than 2,700 degrees Fahrenheit, even though Army officials say the agent is destroyed at 700 degrees.
Army officials dismissed concern Wednesday that with the reduction in Utah's inventory of weapons, more chemical weapons could be shipped to the state for incineration. The Defense Department has been studying a proposal to move weapons from Colorado to Utah.
"As it stands now, there are no plans," said depot spokeswoman Alaine Southworth.
While officials trumpeted Wednesday's occasion, environmental activists cautioned there is much work to be done.
"Well, congratulations," said Steve Erickson, director of the Salt Lake City-based Citizens Education Project. "Let's get rid of the rest of it. The sooner we can get rid of it, the better it will be for all of us."
Since it stores more of the nation's chemical weapons than the eight other incinerator sites, Utah's 63-year-old depot will be the only disposal facility to reach the million-weapon milestone.