Initial construction began from east to west and as bypass loops around larger cities.

By 1967, the highway was complete from the Louisiana state line to the western side of Fort Worth on a route to the south of US 80, with slower construction in the lesser populated areas of West Texas concurrent with US 80.

I-20 begins its eastward journey at a junction with I-10 in a desolate region of West Texas about 6 miles (10 km) east of the town of Kent.

I-20 also generally heads to the east-northeast passing by the cities of Odessa and Midland while transitioning from the West Texas desert to the prairie.

Interchanging with I-35W south of downtown Fort Worth, I-20 heads east toward Dallas passing through Arlington, where it is also known as the Ronald Reagan Memorial Highway.

I-20 leaves the state of Texas near Waskom and just west of the Shreveport, Bossier City, Louisiana area.

Along Texas Interstates, the alphabetic suffixes on business route names ascend eastward and northward.