Flag of the Republic of the Rio Grande
The flag of the Republic of the Rio Grande was used in 1840, during 283 days from January 17 to November 6, as long as the republic existed. This country was formed by the northeastern Mexican states of Coahuila, Nuevo León, and Tamaulipas. The flag was no longer used following the defeat of the Republic of the Rio Grande by Mexican troops. Design

The flag of the Republic of the Rio Grande has a blue hoist with three white stars run evenly along the hoist. The three stars represent the three states that seceded: Coahuila, Nuevo León, and Tamaulipas. The fly is split into three bands, one white, one red, and one black. There are other suggested designs for the flag as noted by historians, including tricolors of (a) red, white, and black; (b) red, white, and blue; and (c) red, white, and green. Historians have noted that, whatever the flag looked like, it bore similarities to the 1839 flag of the Republic of Texas and the 1841 flag of the later Republic of Yucatán. The city of Laredo, Texas uses the black stripe variant of this flag as its city flag, while also incorporating it and the six flags over the rest of Texas on its city coat of arms. Laredo had served as the capital of the brief republic. See also 

 Flag of Texas
 Flag of Mexico

References 

Flags introduced in 1840
Rio Grande
Flags of Texas
Independent Mexico
Mexican Texas
Flag