San Antonio is the second-largest city in Texas. San Antonio had, at one time, been a part of Mexico, but the Mexican influences never disappeared from the city.
 
By at least 1995, San Antonio was being called “the northernmost city in Mexico.” San Antonio itself promoted its Mexican influences by using the “northernmost city in Mexico” tagline in advertisements in the Wall Street Journal in 1996.
 
     
Wikipedia: San Antonio, Texas
San Antonio (pronounced /ˌsænænˈtoʊnioʊ/) is the second-largest city in the state of Texas and the seventh largest city in the United States. Located in South Texas, the city is a cultural gateway into the American Southwest. San Antonio is the seat of Bexar County with a population of 1,328,984 as of the 2007 U.S. Census estimate, as well as the 4th fastest growing large city in the nation from 2000-2006 in terms of percentage. Its metropolitan area has nearly 2 million people and is the 28th-largest metropolitan area in the U.S.
 
San Antonio was named for the Portuguese Saint Anthony, whose feast day is on (June 13) when a Spanish expedition stopped in the area in 1691. The city has a strong military presence—it is home to Fort Sam Houston, Lackland Air Force Base, Randolph Air Force Base, and Brooks City-Base, with Camp Bullis and Camp Stanley right outside the city. Furthermore, Kelly Air Force Base (now Port San Antonio) operated out of San Antonio until 1995. San Antonio is home to the South Texas Medical Center, the only medical research and care provider in the South Texas region.
 
Famous for its River Walk, the Alamo, Tejano culture, and home to the SeaWorld San Antonio and Six Flags Fiesta Texas theme parks, the city is visited by 26 million tourists per year according to the San Antonio Convention and Visitors Bureau. San Antonio is also home to the first museum of modern art in Texas—the Marion Koogler McNay Art Museum, as well as one of the more successful National Basketball Association teams in league history, the San Antonio Spurs. 
 
Visit San Antonio
Texas cooking conjures the tastes of smoky barbeque, spicy chili, and sizzling fajitas. San Antonio, called “the northernmost city in Mexico,” has its own local flavor, melding cuisine from both sides of the border and around the world. More than just Tex-Mex and chuckwagon fare, San Antonio is a hub of culinary creativity inspired by fresh produce and locally raised meats.
 
BNET
San Antonio: `The One Truly Lovely City in the State’
Journal Record, The (Oklahoma City),  Apr 11, 1995 by Jim Auchmutey
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San Antonio isn’t a border town in the strictest sense. One hundred and fifty miles of scrubby prairie lie between it and the Rio Grande crossing at Laredo. But if you forget the map and listen and look and taste, it’s easy to imagine you’re in the northernmost city of Mexico.
 
Red, white and green are everywhere. “Numero Uno hits,” blare the radio disc jockeys in one of the few bits of their Spanglish patter I could understand. “Barbacoa,” say the signs in front of restaurants that serve good old Texas beef barbecue with good old Mexican corn tortillas.
 
4 May 1996, San Antonio (TX) Express-News, “Civic pride ad campaign is puro juat?” by Carlos Guerra:
I have to agree with San Antonio’s tourism czar Steve Moore and his minister of propaganda Steve Atkins.
 
“Pure” is a good, positive word, and ” puro , ” its Spanish translation, is even stronger. Puro juat? you ask.
 
Well, I’ll let you decide. After all, the “civic pride” campaign that was unveiled Friday is being paid for with your tax money.
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In huge—and expensive—ads in the Wall Street Journal, they billed our city as “the northernmost city in Mexico.” They quietly dropped that campaign -...
 
January 2000, American Libraries, “New Southwestern Cuisine: From Tamaleville to Tex-Mix”:
San Antonio’s role in the second coming of Texas cooking has been pivotal. Often referred to as “the northernmost city in Mexico,” it has long been the state’s keeper of culinary tradition.
 
13 May 2001, Denver (CO) Post, “San Antonio No. 1 vacation stop deep in the heart of Texas” by Lee Foster, pg. T8:
With about 55 percent of the nearly 1 million residents of Hispanic origin, San Antonio is sometimes called “the northernmost city in Mexico.
   
The Motorist (July/August 2001)
San Antonio
Texas Favorite Offers the River Walk, the Alamo and Much More
by Tom and Joanne O’Toole
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Sampling the local cuisine is traditional for tourists, and spicy plates of food come in all shapes and sizes. San Antonio is often referred to as “the northernmost city in Mexico,” and is the state’s keeper of culinary excellence. Much of the food is simmered in the tradition of Tex-Mex-a cuisine that captures the flavors from both sides of the border.
       
21 August 2006, Grand Forks (ND) Herald, pg. 9:
Fun Fact: San Antonio sometimes is called “Mexico’s Northernmost City.”
   
The Kennebec Report
March 17, 2007
Ten Things to Like About San Antonio
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9) The Mexican-ness of San Antonio. People told me that San Antonio is the northernmost city in Mexico, and I have no reason to doubt this. Hispanic culture is big here, judging by the number of times and different contexts I saw Our Lady of Guadalupe—looking down benevolently from behind cash registers, painted as a mural on the walls of gas stations, enshrined in statue niches in churches . . . and it wonderful to see the range of skin tones, hear melodic Spanish on the streets, watch big Mexican families come out of church on Sunday, listen to Tejano music at the Public Market, and so on. (The Market didn’t make the list, I regret, because it seemed so tarted up and designed for tourists from Des Moines, or maybe Maine or something. Maybe I need to give it another try, but I didn’t need to invest in any Mexi-kitsch.)