Most habitat for king rails in Missouri is in river bottoms, where shifting channels provide a variety of shallow wetlands. Details of their habitat are poorly known. They feed in water less than six inches deep. Marshes with small hummocks and a variety of water depths should provide for most of a king rail's needs. After spending the winter in southern coastal marshes, king rails may return to Missouri as early as late February, but most arrive by mid-May.
Males typically begin calling to attract mates shortly after arrival.
After pairing, birds begin building nests. This activity usually lasts from mid-May until June, but some birds begin building nests as early as March. In southeastern Missouri, broods have been seen as early as April. Females lay an average of about 11 eggs. Both sexes incubate the eggs, and incubation takes 21 to 23 days.