SAN ANTONIO — In 2008, after 15 years as the Alamo City’s largest corporate resident, AT& T announced it was moving its headquarters to Dallas — and taking 700 executives along with it. In the past, that San Antonio’s first Fortune 500 company had outgrown its home might have seemed an insurmountable blow for this city with a pre-existing inferiority complex. But these days, it is not easy to shake the city’s confidence.

In the last decade, companies have flocked to San Antonio, making it an economic center rivaling Houston and Dallas. With that business expansion has come energetic population growth: according to United States Census numbers, in the past 10 years, San Antonio has added more people within its city boundaries than any other major city in the state. It has all attracted demographers’ attention, at home and across the nation.

“San Antonio is sometimes seen as that sleepy southern city of Texas,” said Steve H. Murdock, a former director of the United States Census Bureau and Texas state demographer. “If you look at its growth, if you look at its changes in the last two decades, it is a city that may be changing more in nature than the other two larger cities.”

San Antonio recently topped the Milken Institute’s annual list of the best-performing cities, a ranking that measures American metropolitan areas based on their ability to create and sustain jobs. The city, which for the past five years has made it to No. 7 among the largest metropolitan areas in the country, has been “incredibly resilient” in the economic downturn, said Kevin Klowden, an economist with Milken, a California-based economic think tank.