John Martin Stadheim was born to Endre Johannes Stadheim (1846 - 1905) and Kari Larsdattir Foli (1851 - 1938). His father was born in Norway and his mother was born in Illinois. He had eight siblings: Berten, Ole Johan, Lissi, Ole E., Johanna, Louis, Clara, and George Stadheim. He also had three half-siblings: Lewis, Tim, and Lissi Stadem.
John Stadheim married Gjorene "Julia" Nummedahl (1869 - 1931) on January 12, 1896 in Freeborn, Minnesota and they had one son, Even J., and one daughter, Mabel Christine Stadheim.