Like a lot of you, I thought it was strange that county judges were issuing shelter-in-place orders. Weirdly enough though, it looks like they are empowered to do that under Texas Government Code Section 418.108. The relevant part is (g).

"The county judge or the mayor of a municipality may control ingress to and egress from a disaster area under the jurisdiction and authority of the county judge or mayor and control the movement of persons and the occupancy of premises in that area."

I had no idea county judges had such sweeping powers. That said, let me know if I'm misinterpreting the statute.