There are many books and articles written about Texas Germans. For an introduction to Texas Germans, the following works are a good place to start.
Boas, Hans C. 2009. The life and death of Texas German. Durham: Duke University Press.
Biesele, Rudolph. 1928. The history of the German settlements in Texas, 1831-1861.
Austin, TX: Press of Von Boeckmann-Jones Co.
Jordan, Gilbert J. 1977. The Texas German Language of the Western Hill Country. Rice University Studies, 63(3), 59-71.
Jordan, Terry. 1977. The German element in Texas. Rice University Studies 63(3): 1–11.
Jordan, Terry. 1975. German Seed in Texas Soil. Austin, TX: University of Texas Press.
Wilson, Joseph. (1977). The German Language in Central Texas Today. Rice University Studies, 63(3), 47-58.
Gilbert, Glenn G. (1972). Linguistic Atlas of Texas German. Austin, TX: University of Texas Press.
Gilbert, Glenn G. (1977). Origin and Present Day Location of German Speakers in Texas: A Statistical Interpretation. Rice University Studies, 63(3), 21-34.