Slightly more elaborate than most Charles Starrett westerns, Down Rio Grande Way is set in the mid-19th century, when the Republic of Texas was poised to join the Union. Starrett plays Texas Ranger Steve Martin, who is dispatched to a "renegade" Texas country that refuses to become part of the good old USA. He discovers that the crux of the problem is a local tax collector who, with the help of a crooked newspaper editor, is systematically robbing the citizens of their hard-earned cash, all the while fomenting anti-American sentiments.

Charles Starrett
as Steve Martin

Russell Hayden
as 'Lucky' Haines

Britt Wood
as Britt Haines

Rose Anne Stevens
as Mary Ann Baldridge

Norman Willis
as Mack Vandall

Davison Clark
as Colonel Elihu Baldridge

Edmund Cobb
as Henchman Stoner

Budd Buster
as Clem Kearney

Joseph Eggenton
as Judge Randolph Henderson

Paul Newlan
as Sam Houston