I referenced several sources including newspapers, other written sources and maps to ascertain the history of the main highway that now takes us from Wichita Falls to Brownsville.

I am only speaking to the stretch as it extends through Burnet County, as it gets much more complicated trying to talk about the entire stretch as it goes from Canada to Mexico.

The photo below is a 1919 map. It doesn’t show an actual road extending from Blanco to Lampasas. (Probably just trails at that time) This map doesn’t show a road from Blanco to San Antonio either.

The next two photos are 1936 maps. They show a completed highway with both Texas 66 and US 281 designations.

The photo below is a post card that shows being at Highways 29 and 65. (I believe the 65 is a typo and should say 66)

The photo below is a 1937 newspaper clipping about a tragic death that happened out around the railroad tracks between Marble Falls and Burnet. (The newspaper writer was still getting use to the renumbering, I suppose?)

The two photos below are Texas 66 Road signs.

These last two photos are US Texas 66 & Route 66, the famous East / West Highway made famous as the great migration route for folks heading West to California seeking fame and fortune. (This highway had nothing to do with the Texas 66 that ran North / South)

This is another web search about the highway:
In 1929, construction of the Burnet County section of State Highway 66 (later U.S. Highway 281) began; the project lasted until 1939.

In conclusion I think there was a somewhat improved road built between 1919 when state funding was starting to be sent to counties to build roads and 1929 when The Texas Highway Department actively undertook to build the highway and named it Texas 66. Then sometime in the next few years the Federal Government got involved building the US Highway System and adopted the US 281 designation.

I have read some place that the first road through Marble Falls was called Highway 3. (or some other single digit designation – may have been 5) I am still looking for the source of that.