Dumingag is a landlocked municipality in the coastal province of Zamboanga del Sur.

The municipality has a land area of 297.75 square kilometers or 114.96 square miles which constitutes 6.64% of Zamboanga del Sur’s total area. Its population as determined by the 2020 Census was 48,881. This represented 4.65% of the total population of Zamboanga del Sur province, or 1.26% of the overall population of the Zamboanga Peninsula region. Based on these figures, the population density is computed at 164 inhabitants per square kilometer or 425 inhabitants per square mile.