A prolific writer, Garland continued to publish novels, short fiction, and essays. In 1917, he published his autobiography, A Son of the Middle Border. The book's success prompted a sequel, A Daughter of the Middle Border, for which Garland won the 1922 Pulitzer Prize for Biography. After two more volumes, Garland began a second series of memoirs based on his diary.
Garland died at age seventy-nine, after moving to Hollywood, California, where he devoted his remaining years to investigating psychic phenomena, an enthusiasm he first undertook in 1891. He was buried in Neshonoc Cemetery in West Salem, Wisconsin. In his final book, The Mystery of the Buried Crosses (1939), he tried to defend such phenomenon and prove the legitimacy of psychic mediums.
Hamlin Garland lived on a farm between Osage, and St. Ansgar, Iowa for quite some time. Many of his writings are based on this era of his life.
The Hamlin Garland House in West Salem is a historical site.