Río Rico is a village located along the Rio Grande in the Mexican state of Tamaulipas. It includes a portion of the Horcón Tract, a narrow 461-acre (1.87 km2) piece of land (including former riverbed) that was north of the meandering river—and thus part of the U.S. state of Texas—until an unauthorized diversion of the river to its north cut it off from the rest of the state in 1906. Río Rico developed as a de facto Mexican settlement, and the international border was moved under the terms of the Boundary Treaty of 1970, placing the tract and the village in Mexico, effective in 1977.