Before the U.S. Route system, this route was a system of interconnected highways from New Mexico to Oklahoma, considered a part of the Texas highway system from New Mexico to Amarillo and a portion of the Ozark Trails.
In Amarillo, the Ozark route split off to a more southerly route, while general low-grade roads continued east.
This entire route closely paralleled the Chicago, Rock Island and Pacific Railway.
 Most construction through the Panhandle was slow, and remained low-grade roads through most of the 1920s.

In 1926, the United States Numbered Highway system was introduced, and the route across the Texas Panhandle was given the number of 66.
 It was designated along already created roads in the Texas highway network.
Large portions of the highway remained earthen roads until the entire route was completely paved in 1938.
 A few realignments were made to the original route.
 A new routing on the east side of Amarillo was completed in 1959 to make way for the expansion of the Amarillo Air Force Base, while the rest of the route through Amarillo was rebuilt on the north side of downtown.
Before the U.S. Route system, this route was a system of interconnected highways from New Mexico to Oklahoma, considered a part of the Texas highway system from New Mexico to Amarillo and a portion of the Ozark Trails. In Amarillo, the Ozark route split off to a more southerly route, while general low-grade roads continued east. This entire route closely paralleled the Chicago, Rock Island and Pacific Railway.  Most construction through the Panhandle was slow, and remained low-grade roads through most of the 1920s.
In 1926, the United States Numbered Highway system was introduced, and the route across the Texas Panhandle was given the number of 66.  It was designated along already created roads in the Texas highway network. Large portions of the highway remained earthen roads until the entire route was completely paved in 1938.  A few realignments were made to the original route.  A new routing on the east side of Amarillo was completed in 1959 to make way for the expansion of the Amarillo Air Force Base, while the rest of the route through Amarillo was rebuilt on the north side of downtown.
U.S. Route 66 in Texas