Establishment by charter
The university charter was laid down by two Presidential Decrees, P.D. 1434 and P.D. 1437. On June 10, 1978, then President Ferdinand E. Marcos issued P.D. 1434 which established the Isabela State University by merging the Isabela State College of Agriculture (ISCA) at Echague, the Cagayan Valley Institute of Technology (CVIT) at Cabagan, and absorbing the college courses of the Isabela School of Arts and Trades (ISAT) in Ilagan, Roxas Memorial Agricultural and Industrial School (RMAIS) in Roxas, San Mateo Vocational and Industrial School (SMVIS) in San Mateo and Jones Rural School (JRS) in Jones, Isabela. The merger likewise identified Echague to serve as the main campus and administrative site.