When Margaret Williamson left her family's rural Wisconsin farm to work in Minneapolis in 1923, her mother, Olava, wrote regularly with updates about daily activities: laundry, bread baking, plowing, planting, and harvesting the crops. Sometimes she enclosed a note from seven- year- old Helen, who reported on school and shenanigans and how she longed to see Margaret again.

So begins decades of stories about a family at once singular-- with personal joys and challenges-- and broadly representative of the countless small farms that dotted the midwestern landscape in the early...