I have found corns on the roads north of Franklin about 50-60 miles east of Temple. I suspect they are in the sandy woodlands east of I-35 as well. There should be speckled kings and milksnakes around there as well since I have found both around Franklin. Actually, April and May is a good time for milks on the roads in that part of Texas.
The hilly rocky country around Killeen isn't great for either of those species.
If I was looking for these species around your area I would try hunting some of the roads over towards Rosebud and similar areas. I haven't ever been there, but I've found all your target species near Calvert on the other side of the Brazos River.
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Chris Harrison
San Antonio, Texas