San Ysidro is a district of San Diego, California, forming the city's southernmost reach immediately north of the Mexico–United States border. It is not a separate incorporated city but a distinct community within San Diego, annexed by the city in 1957. Its name, meaning "Saint Isidore" in Spanish, reflects the region's Californio heritage and the binational identity that defines the district today. San Ysidro's defining feature is the San Ysidro Port of Entry, the land border crossing between San Diego and Tijuana and the busiest such crossing in the Western Hemisphere, handling tens of millions of crossings each year. The crossing traces its roots to the late 19th century, with the modern facility built in 1932. That constant flow of people and commerce has made San Ysidro one of the most heavily trafficked and culturally dynamic communities in the country. With roughly 27,000 residents, San Ysidro is a dense, predominantly Latino and Spanish-speaking district where apartment buildings and single-family homes sit close to commercial corridors and the border itself. Most households rent, and the streetscape is a busy mix of retail, transit, and residential life. The district borders Otay Mesa West to the north, Otay Mesa to the east, and Nestor and the Tijuana River Valley to the west, anchoring San Diego's southern border region. Transit and geography shape daily life. The San Ysidro Trolley Station is the southern terminus of the San Diego Trolley's Blue Line, running directly to downtown San Diego, while Interstate 5 feeds the port of entry and connects the district to the wider city. Students attend the San Diego Unified School District. For its residents, San Ysidro is a place of deep cross-border ties, where two countries meet on a single street.