Hermann married future U.S. Representative Bill Emerson, a Republican from Cape Girardeau, on June 22, 1975. They had two daughters; Jo Ann also has five stepdaughters and a stepson. Bill was elected to the U.S. Congress in 1980 from Missouri's 10th Congressional District and, subsequent to redistricting, was reelected in 1982 from the 8th District. He died from cancer on June 22, 1996, a few months before the end of his eighth term. The Bill Emerson Memorial Bridge, which links Missouri to Illinois across the Mississippi River, was dedicated to commemorate his efforts to obtain federal funding for its construction.