The route continues as Texas Park Road 100 east and north to a dead end on South Padre Island.

SH 100 was designated on September 15, 1924 on most of its current routing in Deep South Texas, but it ended at Gomez Street in Port Isabel.

[3] Since its initial construction, the only two changes in the routing was on January 23, 1975, when SH 100 was extended east 0.5 miles replacing the section of PR 100 from Gomez Street to the western end of the Queen Isabella Causeway, and that SH 100 was rerouted the city of Port Isabel, where the route was transferred to separate one way surface streets to better handle flow onto the Queen Isabella Causeway SH 100 begins at an intersection with Interstate 69E/U.S.

Continuing southeast, it passes through the town of Laguna Heights, before reaching the city of Port Isabel.

It reaches its eastern terminus at the Queen Isabella Causeway, which continues across the Laguna Madre to South Padre Island as Texas Park Road 100.