The Southernmost Boundary of the United States: The US–Mexico Border

The southernmost land boundary of the United States is the international border with Mexico.

• Length: ~1,954 miles (3,145 km)
• Western terminus: Pacific Ocean (Border Field State Park, CA / Tijuana, BC)
• Eastern terminus: Gulf of Mexico (Boca Chica, TX / Matamoros, Tamaulipas)

The boundary follows the Rio Grande (Río Bravo) for ~1,250 miles, then cuts west overland through deserts, mountains (Chihuahuan, Sonoran), and urban areas (San Diego, El Paso, Laredo, Brownsville).

It is the world's most crossed land border (~350 million legal crossings/year pre-pandemic), vital for trade (USMCA), migration, and binational communities.