Texas German descended from a group of dialects spoken by the early German settlers in Texas. Immigration from Germany to the northern coast of the Gulf of Mexico began in the 1840s. Texas German is not a single dialect, and it is spoken differently in different areas of Texas. It is a mixture of the dialects that the original German immigrants spoke, combined with English and some natural language change over time.
The images below are from Terry G. Jordan (1977) The German Element in Texas: An Overview.