San Marcos's 2026 population is now estimated at 59,133. In 2007, the population of San Marcos was 63,209. San Marcos experienced a decrease of -239 residents over the past year, marking an annual decline of -0.4%. These population values and projections come from DIGESTYC Censo de Poblacion y Vivienda 2007 poblacion por municipio and ONEC-DIGESTYC proyecciones municipales de poblacion 2020-2030 revision 2021 .