SC 12 Augusta GA to Columbia 1926 Official

US 1 replaces SC 12 1930 Official

SC 50 from Columbia to North Carolina via Camden and Cheraw 1922 Auto Trails

SC 50 becomes US 1 1927 Clasons

Adjustments: About 1927, US 1 was put on its modern routing between McBee and Patrick, bypassing Middendorf. US 1 had used S-13-63 to Middendorf; unpaved Middendorf Church Rd; S-13-29 to McKennon; unpaved TT 10 Rd which no longer crosses the RR back to US 1 below the Cow Creek Bridge in Patrick
In 1928, the SC 12 and SC 50 designations were dropped from US 1. SC 2 however remained.
It is possible US 1 briefly used today's S-2-67 Anthony Dr in Bath and S-2-225 Dibble Rd west out of Aiken but definitely stopped doing so by 1928.
About 1929, US 1 was put on modern US 1 routing through Kershaw County. US 1 had been using S-28-102 to Elgin; S-28-21 Smyrna Rd; S-28-349 Wildwood Ln; SC 34 to Lugoff
About 1932, US 1 was put on its modern routing from Patrick to Cheraw. US 1 had been using McLain/Griggs/Emma Rd out of Patrick; abandoned alignment east of US 1 connecting with S-13-232 through Cheraw State Park; abandoned routing to connect to Old Cash Rd then Howard Alley/2nd St to Cheraw.
US 1 was removed from Hayne St (remained part of US 78/SC 215 and is now S-2-3) and York Ave (remained part of US 78 and is now S-2-31) in Aiken in Oct 1937 (SCDOT).
In 1939, US 1 was rerouted in Cheraw and eastward to meet the new Pee Dee River bridge that US 1 still uses today. The old route may have briefly been US 1 ALT. Today it is 2nd St and Church St and on the other side of the river it is S-35-36.

US 1 original Pee Dee crossing 1937 Official

US 1 on new alignment to the north 1939 Official

About 1946, US 1 moved in Columbia to use Gervais, Harden, then Taylor to Two Notch.
In 1951, US 1 moved in Columbia to use Gervais to Millwood to Two Notch.

US 1 original Columbia 1932 Texaco

US 1 moved to use Harden-Taylor 1942 Richland County

US 1 moved to use Millwood 1951 Official

In 1951, US 1-78 was given a new alignment to bypass Clearwater, Bath, and Gloverville leaving behind SC 421.

US 1-78 through several towns 1950 Official

SC 421 replaces US 1-78 1951 Official

Around 1957, US 1-78 was moved off the 5th St bridge over the Savannah River to Augusta onto its current alignment a little south. The old route is now US 1 CONN.
Improvements: Upon designation, US 1 was paved Augusta to Aiken and Columbia to Lugoff.
In 1929, US 1 was paved from Aiken to Columbia and Lugoff to Bethune.
In 1931, US 1 was paved from Bethune to Patrick.
The remaining piece of US 1 from Patrick to the North Carolina line was paved in 1932.
The first piece of US 1 to be 4-laned was the first couple miles north out of Columbia, about 1940.
By 1946, US 1 was multilaned in West Columbia.
The new alignment from Augusta to Aiken was 4-laned upon construction in 1951 or 1952.
In 1960, US 1 was multilaned from Camden to about a mile past SC 34 EB split.
In 1961, US 1 was multilaned on its US 52 and SC 9 duplexes
By 1963, US 1 was multilane through Columbia.
In 1968 or 1969 US 1 was 4-laned from Lugoff to Camden.
In 1970, US 1 was 4-laned northeast to I-20 in Columbia.
In 1972, US 1 was 4-laned from W. Columbia west to I-26.
In 1973, US 1 was 4-laned from I-26 west to I-20.
In 1974, US 1 was 4-laned from I-20 to I-77 and from I-20 west to Lexington.
In 1975, US 1 was 4-laned on its Lexington US 378 duplex.
In 1976, US 1 was 4-laned west of the US 1-378 split to S-32-204.
In 1978, US 1 was multilaned from I-77 to Pontiac.
In 1997, US 1 was 4-laned from Aiken north to I-20.
In 2001, US 1 was multilaned from S-32-204 west to S-32-24 near Gilbert.
In 2016, US 1 was multilaned from S-32-24 west to S-32-31 near Summit.
In 2023, US 1 was multilaned from S-32-31 Summit west to SC 23 Batesburg-Leesville
Truck Route: There is a signed US 1 TRUCK in Aiken that follows SC 118. This has been around since at least the 1980s.
There is another signed US 1 TRUCK in Cheraw, using Manor Rd, Cash Rd, and Front St. Been around at least 10 years.
Comment: US 1 has undergone relatively little change in its lifetime in South Carolina.
South Carolina is the middle of three states where US 1 doesn't hug I-95. However, in general it is treated as a minor route in SC unlike North Carolina and Georgia which have widened almost all of it.
Other than the Lexington to Pontiac section, US 1 is an easy, wide open drive.