We put in a large pond last summer. the frogs came in late February. There have been at least 10, including a large bullfrog that has been in it's spot daily for the past month. Yesterday, during a rain they all left. Will they return, and where did they go?

When it rains, that makes it easier and safer for frogs to travel as they must stay moist when they walk around. They probably went out to see what other water sources they could find. If they go too far and don't find any, they can dessicate and die from lack of water. But, most will find a puddle or pond and once refreshed continue on until they find a place to hang out. If they decide that your pond was a nicer home, they will return. It may not happen until it rains a lot again. I have a lot of frogs that come and go as they please.