There's apparently a pocket of German-speaking Texans who have developed their own dialect. These are descendants of German settlers who came to America probably in the last 150 years or so.http://www.bbc.co.uk/news/magazine-22490560
I am surprised you have never heard of it. They are centered around Fredericksburg and just south of San Antonio. They are called Texas Deutsche and my wife (a Native German) can barely understand them. It is neat though because you can get German food with a Texas flair in the area.Maybe I just know it because I lived in Texas so long and assumed it was common knowledge.
I lived in Texas for a while as well but it was closer to North Texas. I might have heard that an area further south had German descendents in it, but I didn't know that they preserved their own dialect.
I have read that Texas Deutsche as a dialect is dying out. In fact, I read a piece about a year or so ago about a linguist at UT who us trying to get it recorded before all the native speakers die out.
The work by that UT researcher is exactly what the article/video is about that I linked to in the original post. He's trying to document it before the people die out.