International Boundary Marker No. 1, U.S. and Mexico, Boundary marker in Doña Ana County, New Mexico, United States.

The International Boundary Marker No. 1 is a boundary monument between Mexico and the United States located near Sunland Park in New Mexico. It consists of a tall stone pillar with a square base that marks the western land section of the international border.

The 1848 Treaty of Guadalupe Hidalgo set the Rio Grande as the border east of El Paso but left the western land boundary undefined. From 1848 to 1853 William Hemsley Emory and the Emory–Salazar Commission surveyed roughly 3,200 km of uncharted terrain. The commission placed this dressed stone marker in 1855 where the border leaves the river and runs west overland, the first marker on that stretch.

The marker stands where the Guadalupe Hidalgo boundary leaves the Rio Grande and runs west over land, the first monument of that land section. It also commemorates the U.S. surveyors who fixed the line, work done by William Hemsley Emory and the Emory-Salazar Commission across roughly 3,200 km between 1848 and 1853.

The monument is located near Sunland Park and remains visible and accessible from the nearby roads. Access is easiest via McNutt Road in the southern section of the area.

The 1966 refurbishment stripped the monument's old plaster coating down to the original masonry and re-faced it with white marbleized concrete, adding a 9 by 9 metre concrete slab platform. In June 2019 the IBWC found that We Build the Wall had built a gate across the road to the marker without permits; the dispute was resolved and the gate is now open by day and locked at night.