I've already told you about the Family History Library at BYU and the Gardens at Thanksgiving Point. I'm going to give you a few other places to make a day trip out of Utah County. I think the Family History Library and the gardens would be the perfect day. So I'm pretty much just going to give you a few places to eat.
Thanksgiving Point has a really good restaurant called the Harvest Restaurant. It has fresh good food and the walls of the restaurant are painted with fun "trompe l'oeil" art on the walls. Right next to Thanksgiving Point is another favorite burger place--JCW's. A little further south on the BYU campus is the Museum of Art Cafe. The Cafe is only open from 11 to 2 for lunches, but they have wonderful salads and an amazing cold raspberry soup. Other fun places to stop include Cabelas where you can see the wildlife displays and aquariums and dine on buffalo or ostrich at the High Uintas grill. And if you ever come later in the fall, the most beautiful place on earth to see the leaves change is the Alpine Loop drive between American Fork Canyon (stop and see Timpanogos Cave) and Provo Canyon (home of Sundance Ski Resort).