Along with the title, crown and sash, she received $100 and a dozen red roses.
Waltemire came close to her dream last year, when she was named first runner-up her first time competing.
Still, she didn't think she had it cinched this year, she said.
"It was a total shock," said Waltemire, an incoming senior at South Hagerstown High School. "I'm very happy."
She said she plans to take an aggressive approach to her spokeswoman role.
"I want to do as much as I can to get more people to come," she said. She said she especially looks forward to helping her friends with their animals at the Ag Expo each year.
Waltemire said she plans to work closely with the Ag Expo board so she can benefit from their ideas.
She said she'll push local businesses leaders to come out to the Ag Expo to learn more about it and support its events.
And she'll do her best to get the word out to the public, she said.
Waltemire competes in volleyball, basketball and softball and has been active in her school's student council, French club, scholarship and homecoming committees.
A 4-H member, she submitted a variety of baked goods - including coconut cake, chocolate fudge, chocolate chip cookies and fruit muffins - at this year's Ag Expo competition.
First runner up for the Ag Expo Queen title was Laura Schmidt, 16, the daughter of Donna and Barry Schmidt. She is entering her junior year at South Hagerstown High School.
Second runner up was Jessica Leatherman, 15, daughter of Debbie and Jim Leatherman. She is entering her junior year at Boonsboro High School.
Ag Expo is being held all this week at the Agricultural Education Center, off Md. 65, Sharpsburg Pike, 10 miles south of Hagerstown.