Toward the end of season 3 the Andersons visited Margaret's parents because her father had some unspecified illness due to his work at his printing shop. They didn't mention the town.

Earlier they were going to Lemon Falls (and also in a later episode) for her family reunion.

At the beginning of season 4 Margaret's parents deeded to Margaret a house they owned, and rented out, in Springfield. She mentioned they live in Hillsboro.

If her people went to Lemon Falls for reunions wouldn't it be logical to think her parents lived there?

Hmm, they may have gone to whatever relative had the biggest house to hold the reunion.

I thought it was her aunt that lived in Lemon Falls?

I think that's Aunt Ione (spelling? Give that one to Kathy in the spelling bee...). She lives in some other town, and they sometimes have (in the past) picked her up on the way to Lemon Falls, even though Jim complains she lives in the opposite direction.

Neither here nor there, but in both family reunion episodes Jim and Margaret were fighting, both times over the fact that none of the Andersons wanted to go.

I remember the one episode where Jim, Betty, and Bud were acting out how their relatives acted during a reunion. Margaret did not find their acting very funny.

Maybe Lemon Falls was a suburb of Hillsboro or vice versa.