Eagle Ford Shale drilling in concentrated in the counties below.
The play varies in depth as it heads south towards the gas window. An overview of the play can be found here.

Counties
Atascosa County,TX - Eagle Ford Shale Drilling
Bastrop County,TX - Eagle Ford Shale Drilling
Bee County,TX - Eagle Ford Shale Drilling
Brazos County,TX - Eagle Ford Shale Drilling
Burleson County,TX - Eagle Ford Shale Drilling
Colorado County,TX - Eagle Ford Shale Drilling
De witt County,TX - Eagle Ford Shale Drilling
Dimmit County,TX - Eagle Ford Shale Drilling
Fayette County,TX - Eagle Ford Shale Drilling
Frio County,TX - Eagle Ford Shale Drilling
Gillette County,TX - Eagle Ford Shale Drilling
Gonzales County,TX - Eagle Ford Shale Drilling
Grimes County,TX - Eagle Ford Shale Drilling
Karnes County,TX - Eagle Ford Shale Drilling
La salle County,TX - Eagle Ford Shale Drilling
Lavaca County,TX - Eagle Ford Shale Drilling
Lee County,TX - Eagle Ford Shale Drilling
Leon County,TX - Eagle Ford Shale Drilling
Live oak County,TX - Eagle Ford Shale Drilling
Madison County,TX - Eagle Ford Shale Drilling
Maverick County,TX - Eagle Ford Shale Drilling
Mc mullen County,TX - Eagle Ford Shale Drilling
Mcmullen County,TX - Eagle Ford Shale Drilling
Milam County,TX - Eagle Ford Shale Drilling
Robertson County,TX - Eagle Ford Shale Drilling
Walker County,TX - Eagle Ford Shale Drilling
Webb County,TX - Eagle Ford Shale Drilling
Wilson County,TX - Eagle Ford Shale Drilling
Zavala County,TX - Eagle Ford Shale Drilling