ERCOT has been operating the Texas power grid since 1996, and it has overseen the retail electricity market since it launched in 2002.
According to ERCOT’s website, it covers around “75% of the land area in Texas,” including major population centers like:
Houston
Dallas/Fort Worth
San Antonio
Austin
It doesn’t extend to Northeast Texas, Southeast Texas, or the El Paso region. These areas are connected to other grids outside of the state.