Many of them admitted to being there to see Alabama farmer Wayne Keith's wood-burning pickup truck.
Another 300 people attended on Sunday, not including 100 vendors who set up displays focusing on "green" living.
Vendors sold locally produced honey, hemp clothing, preserves, home-spun wool scarves, goats-milk soap, heirloom seeds and organic produce.
Larger displays included outdoor wood-burning furnaces, solar energy information and well buckets made of PVC pipe.
"Feedback from people attending and vendors has been excellent," Mike Slack, one of the event organizers said. "One local dairy goat breeder said it was the best event of its kind she had attended. Several vendors said they definitely will return next spring."
The event is the third one held in Thayer. The first one was two years ago, followed by an April event next to the city pool.
Go Green Ozarks has a multiple mission -- promoting use of new clean technologies and renewable energy like wood, wind, solar wind and bio-fuel to help our local economy; promoting natural healthy food production which benefits the consumer and the farmer; and doing business in our local economy making it sustainable, according to the group's mission statement.
"Every dollar spent locally circulates 10 times, creating and stabilizing jobs and business," Slack said. "The Go Green Festival was very successful in this."
Slack's wife, Deb Slack, who presented a program on organic gardening, gave an example of one man who made a deal to sell chickens and delivered them to his customers at the festival.
While there, the chicken farmer picked up three more customers, delivered those chickens on Sunday, picked up two more customers on Sunday and will deliver those this week.
"He also made a deal with a local farmer to raise chicks in the spring to sell. Another farmer made a deal to sell a whole beef to a couple looking for natural, grass-fed beef," Deb Slack said. "That's what Go Green is all about."
Even the barter system returned. People were trading vegetables, flowers and crafts for canned jams, jellies and pickles, she said.
The Ministerial Alliance of Thayer-Mammoth Spring, with members in Alton and other towns, sponsored activities for children.
One popular event was "Money in a Hay Bale." On both days, youngsters scrambled to tear up bales of hay full of coins. Afterward, not a coin was found, and the hay was raked up and recycled, being fed to cattle after the event.
Speaker Doreen Hannes, the Freedom Farmer, answered dozens of questions on food freedom, the dangers of the National Animal Identification System and abuses of the farming community and natural food producers by the federal government, with suggestions for county control of food freedom rights.
Robyn Gilbert, an expert on healthy foods and herbs and their relationship to illness, spoke for two hours, followed by solar-power expert Craig Wiles, who explained how to get "off the grid on a budget."
The most popular event was Keith's firewood-powered pickup truck.
The owner-builder showed off the truck and answered questions for a full eight hours Saturday before driving to Alabama, powered by local oak.
Entertainers included the bluegrass band Signal Hill, the Reparatory Theatre of the Ozarks performing artists, country singer Randy Johnson of Koshkonong and belly dancers Bashirah Nawal and Cashmir of Mountain View.
Organizers said they plan to have another festival in April, although a date has not yet been set.