Sinkhole risk in Johnson County, TX: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 18%
At or near the surface: 18%
Buried under cover: 0%

What to do about a house in Johnson County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 131 of Johnson County's 725 square miles on soluble rock, 131 of them with the rock at or near the surface. With about 210,547 residents (290 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 328 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Johnson County

The nearest county rated sinkhole country is Baylor County, TX, about 137 miles northwest. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Somervell County, TX 26 mi southwest · 35% at surface
Hood County, TX 27 mi west · 42% at surface
Tarrant County, TX 27 mi north · 41% at surface
Hill County, TX 31 mi southeast · 22% at surface
Ellis County, TX 33 mi east · 33% at surface
Bosque County, TX 37 mi southwest · 26% at surface

What Johnson County is built on

The largest mapped soluble unit here is the Grayson Marl and Main Street Limestone, undivided (mudstone), Early Late Cretaceous and Late Early Cretaceous in age, covering about 18% of the county. Next is the Duck Creek Limestone at under 1%.

Against the rest of Texas

Johnson County ranks 104 of 254 in Texas for soluble rock at the surface, and sits above 73% of US counties on that measure.