Texas is a state located in the southern and southwestern regions of the United States of America. With an area of 261,797 square miles (678,051 km²) and a population of 23,507,783 (based on a 2006 U.S. census bureau estimate) in 254 counties, the state is second-largest in both area (behind Alaska) and population (behind California). About half the state's population resides in either the Dallas–Fort Worth or Houston metropolitan areas.
The state's name derives from táyshaʔ, a word in the Caddoan language of the Hasinai, which means "friends" or "allies". Texas declared its independence from Mexico in 1836 and existed as the independent Republic of Texas for nearly a decade. In 1845, it joined the United States as the 28th state.
Texas is internationally known for its energy and aeronautics industries, and for the ship channel at the Port of Houston—the largest in the U.S. in international commerce and the sixth-largest port in the world. The state is home to the most Fortune 500 companies in the United States and has the second-largest economy in the United States, behind California. The Texas Medical Center in Houston contains the world's largest concentration of research and healthcare institutions.