Allen is on U.S. Highway 75 eight miles southwest of McKinney in southwestern Collin County. The town was established in 1870 by a purchasing agent for the Houston and Texas Central Railway and named in 1872 for Ebenezer Allen, former attorney general of Texas and a promoter of the railroad. In 1876 a post office opened there. Four years later Denton outlaw Sam Bass supposedly committed the first train robbery in the state at Allen. By 1884 Allen had a population estimated at 350, three churches, a school, a chair factory, and a flour mill. In 1908 the Texas Traction Company built an electric railway through the town. The population had increased to 550 by 1915. In the mid-1940s the number of residents declined to 400, and in 1948 train service was discontinued. Beginning in the late 1960s, however, Allen's population grew rapidly. Between 1970 and 1980 the number of residents jumped from 1,940 to 8,314. This increase was influenced by the economic growth of Dallas and nearby Plano and the construction of Dallas-Fort Worth International Airport. In 1990 Allen had a population of 18,309 and was the third largest town in Collin County. In 2000 the town's population grew to 43,554.