San Simon is a landlocked municipality in the coastal province of Pampanga.
The municipality has a land area of 57.37 square kilometers or 22.15 square miles which constitutes 2.87% of Pampanga's total area. Its population as determined by the 2020 Census was 59,182. This represented 2.43% of the total population of Pampanga province, or 0.48% of the overall population of the Central Luzon region. Based on these figures, the population density is computed at 1,032 inhabitants per square kilometer or 2,672 inhabitants per square mile.