In 1998 Texas overtook New York as the nation's 2nd most populous state. Between 1990 and 2000 Texas's population grew from 16,986,510 to 20,851,820, a gain of 22.8%, and the 2nd-largest increase for the decade among the 50 states. The state had placed 4th in the 1970 census, with a population of 11,196,730, but had surpassed Pennsylvania in 1974. The estimated population as of 2002 was 21,779,893, an increase of 4.5% since 2000. The population is projected to reach 27.2 million by 2025. The population density in 2000 was 79.6 persons per sq mi.

At the first decennial census of 1850, less than five years after Texas had become a state, the population totaled 212,592. It reached 1,600,000 by the early 1880s (when the state ranked eleventh), passed 4,000,000 during World War I, and jumped to 7,700,000 in 1950. The slowest period of growth occurred during the Depression decade (1930–40) when the population rose only 10%, and the state was surpassed by California. The growth rate ranged between 17% and 27% for each decade from the 1940s through the 1970s; it was 19.4% between 1980 and 1990.

The Texas population has grown steadily older, a phenomenon linked to declining birthrates and increased life expectancies. In 1870, only one out of 68 Texans was 65 years of age or older; by 1990, the proportion was one out of 10. In 2000, the median age for Texans was 32.3. In the same year, 28.2% of the populace were under age 18 while 9.9% were age 65 or older.

The largest metropolitan area in 1999 was Dallas-Fort Worth (which traded places with Houston-Galveston-Brazoria in the national rank of the most populated metropolitan areas from 1980 to 1990), with an estimated 4,909,523 people. Close behind was the Houston-Galveston-Brazoria area, with 4,493,741 residents. San Antonio had an estimated 1,564,949. Houston, the largest city proper in Texas and 4th-largest in the US, had an estimated 2002 population of 2,009,834. Next was Dallas, with 1,211,467; followed by San Antonio, 1,194,222; Austin, 671,873; El Paso, 577,415; Fort Worth, 567,516; Arlington, 349,944; and Corpus Christi, 278,520. With the exception of El Paso, in the far western corner of the trans-Peco region, most of the larger cities are situated along the Gulf coast or on or near an axis that extends north-south from Wichita Falls to Corpus Christi, in the heart of the Blackland Belt.