Daisy is not a real cow, but a Fiberglas training bovine, used to teach children how to milk cows.
Her owner, Jeff Robinson of TileCroft Farms, says someone took the 55-kilogram cow sometime overnight last Thursday.
Robinson says two students set it up on Thursday evening and when they returned the next morning it was gone.
He says he thought it was just a prank, but a search of the fairground came up empty.
Robinson says he doesn't plan to pursue legal action if Daisy is returned.
"It's pretty disappointing that this happened," he said. "It's a needless thing to do."
"There's nothing you can do with that cow," Robinson said Tuesday. "You can't sell it, or anything like that."
The cow, which was built in New Hampshire, would cost about $7,500 to replace.