At the conclusion of the war, President Woodrow Wilson appointed Jadwin to investigate conditions in Poland in 1919. This assignment was followed by an observer assignment in the Ukraine. From 1922 to 1924, Jadwin headed the Corps' Charleston District and Southeast Division. He then served two years as Assistant Chief of Engineers. As Chief of Engineers he sponsored the plan for Mississippi River flood control that was adopted by the United States Congress in May 1928. Jadwin retired as a lieutenant general on August 7, 1929.