The St. Louis, Brownsville and Mexico Railway Company was chartered on June 6, 1903, to run from Sinton to the Rio Grande at Brownsville, with a branch extending westerly to the southeast corner of Starr County, a total distance of 200 miles. The company's charter was amended on various dates to provide for an extension from Sinton to Houston and for the construction of branch lines to Collegeport, Victoria, Port O'Connor, and Sam Fordyce. It was intended that the railroad form one of the sections of a continuous line from Chicago, St. Louis, and Memphis to Baton Rouge, Houston, Brownsville, Tampico, and Mexico City. Initial capital for the company was set at $1,000,000. The principal place of business was Kingsville; the company had temporary offices in Corpus Christi at the time of the charter. Members of the first board of directors were Robert J. Kleberg II and Arthur E. Spohn, both of Corpus Christi; Robert Driscoll, Jr., Uriah Lott, and Richard King, all of Nueces County; John G. Kenedy, James B. Wells, Francisco Yturria, and Thomas Carson, all of Cameron County. Uriah Lott was named first president of the St. Louis, Brownsville and Mexico.
The railroad was built by a syndicate, the principal members being Benjamin F. Yoakum and his associates, managed by the St. Louis Trust Company. The syndicate had hearty cooperation all along the line in land donations and cash bonuses, receiving in all 90,000 acres and $190,000. Citizens of Brownsville and Bay City gave $40,000, while the Calhoun County Cattle Company donated $150,000. Henrietta King gave 75,000 acres of land in Cameron and Kleberg counties, 640 acres for the townsite of Kingsville, and forty acres for shops. All of these donations proved profitable to the donors through the enhancement of their other properties. Construction began at Robstown in August 1903, and the 142 miles to Brownsville opened on July 4, 1904. Sinton was reached on April 10, 1905; Bay City on April 10, 1906; and Algoa, 343 miles from Brownsville, on May 28, 1907. From Algoa to Houston the company secured trackage rights over the Gulf, Colorado and Santa Fe Railway Company. The line was opened through from Houston to Brownsville on December 31, 1907. A branch line from Harlingen through Mission to Sam Fordyce, fifty-five miles in length, was constructed between May and December 1904. Other lines built included thirty-eight miles between Bloomington and Port O'Connor, which opened on March 1, 1910; Buckeye to Collegeport, nineteen miles, which opened in 1911; thirteen miles from Bloomington to Victoria, which opened on May 1, 1912; and the line from Heyser to Austwell, seventeen miles, which opened on October 1, 1912. On July 1, 1912, the company purchased the San Antonio and Rio Grande Valley Railway, an unincorporated line operating between San Juan and Edinburg. At the end of 1912 the St. Louis, Brownsville and Mexico owned and operated 502 miles of main track. Control of the railroad was exercised by the St. Louis Trust Company until May 26, 1910, when the line was sold to the St. Louis and San Francisco Railroad Company for the account of the New Orleans, Texas and Mexico Railroad Company. In 1916 the St. Louis, Brownsville and Mexico reported passenger earnings of $1,560,000 and freight earnings of $2,300,000 and owned fifty-six locomotives and 1,808 cars.
In 1920 the company extended its Brownsville Belt Line two miles from Slinkert to Rio Grande Ranch. Other extensions included nearly eight miles between Faysville and Edinburg, thirty-two miles between Raymondville and Monte Christo, and eleven miles between Hargill and Ed Couch, all opened in 1926. The nineteen miles between Raymondville and Santa Monica opened in 1928, and eleven miles between Ed Couch and Weslaco were completed in 1931. This gave the railroad a total of 585 miles of track. In 1941 the line acquired six miles from the Port Isabel and Rio Grande Valley Railway Company around Brownsville. In 1933, however, the company abandoned thirty-four miles of track between Buckeye and Collegeport and between Lela Pens and Port O'Connor. The railroad also owned a 25 percent interest in the Houston Belt and Terminal Railway Company and a 50 percent interest in the Brownsville and Matamoros Bridge Company. The St. Louis, Brownsville and Mexico became part of the Missouri Pacific Lines on January 1, 1925, but continued to operate as a separate company until it was merged into the Missouri Pacific Railroad Company on March 1, 1956. At the end of 1955 the company owned or leased ninety-eight diesel units and 4,377 cars. In that year it had passenger revenues of $461,554 and freight earnings of $15,759,273. All of the branch lines of the former St. Louis, Brownsville and Mexico in the Rio Grande valley have either been abandoned or sold. The line between Harlingen and Mission is operated by the Rio Valley Switching Company, and the track between Mission and Sam Fordyce is now part of the Border Pacific Railroad.