San Alejo's 2026 population is now estimated at 16,727. In 2007, the population of San Alejo was 17,598. San Alejo experienced a decrease of -65 residents over the past year, marking an annual decline of -0.39%. 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 .