According to U .S. Census Bureau estimates, the number of people in Texas continues to increase year by year. As the state population increases, it is also aging. The Census Bureau estimates that the percentage of the state’s population under the age of 18 has been slowly decreasing since the 2000 Census. According to the Census, the under 18 population accounted for 25.7 percent of the state’s population in 2000, but dropped to 24.3 percent of the total by 2008.

The accompanying map shows that as of 2008 the statewide percentage of those under 18 years old includes a wide variance across the counties. In the two counties with the lowest percentage, Loving and Concho, children account for less than 15 percent of the population (9.5 and 13.0 percent respectively). Yet in Hidalgo, Starr and Webb counties over 35 percent of the population is under 18 (35.8, 36.6 and 37.4 percent respectively).

Another striking feature about the map is that it reveals that the majority of the counties with more than a quarter of the population under 18 lie in three distinct areas. The most prominent of these areas is “T” formed by the I-35 corridor and the eastern half of the international border with Mexico. This formation is not contiguous as Hill County just missed out on being included at 24.6 percent under age 18. Nor does it include every county through which I-35 passes, as Comal and Hays counties are bypassed. However, the inclusion of Caldwell, Gonzales and Guadalupe prevents a second break in the formation.

A second grouping occurs along the Texas-New Mexico border stretching north from Crane and Ward counties to the Texas-Oklahoma border, where it extends eastward as far as Hemphill and Lipscomb. It is between the “T” formation and this west Texas grouping that the majority of the counties with the lowest percentages of children can be found.

A third group of high-percentage counties are located around the Houston-Galveston area. Although smaller in geographic area, some of the state’s most populous counties can be found in this group, including Harris, the state’s most urban county.

One last feature to note about this map is that of the 17 counties with at least 30 percent of the population under 18 years old, all but four are located on either the border with Mexico or the border with New Mexico. The following table shows the ratio of selected age brackets to the total population of the state for the current decade.