So by law it is the authority of the commissioners court to devise or enact a regulation. It was brought to commissioners court and voted against. Which means that there are no regulations relating to land size or distance regarding discharge of firearms. Many people only see the title that applies to municipalities or counties with a certain number population.
You have to read the whole title and chapters to get a good understanding of these regulations.
http://www.statutes.legis.state.tx.us/Docs/LG/htm/LG.235.htm#235.022