Ranch to Market Road 1623 (RM 1623) is a 23.386-mile (37.636 km) farm to market road in Gillespie and Blanco counties, Texas.

[2] It travels to the south into Stonewall, where it crosses Ranch Road 1, and has a one-block eastward concurrency with US 290 before continuing southward.

It then turns to the southeast and crosses into Blanco County.

[4] The RM 1623 designation ends at US 281 in central Blanco; the roadway continues as Loop 163.

Its length was extended to 10.3 mi in 1953 and increased again in 1954; the designation ended at the Gillespie County line.