The province was represented as a lone legislative district until 1972. It was part of the representation of Region II from 1978 to 1984, and from 1984 to 1986, it elected 3 assemblymen at-large. In 1986, it was redistricted into four legislative districts.
On September 27, 2018, PresidentRodrigo Duterte signed Republic Act No. 11080,[1] increasing the legislative districts from four to six and reapportioned the district assignments of cities and municipalities.[2]
^ a bIndependent component city since July 4, 1994. Independent from the province and does not vote for provincial officials by virtue of Republic Act No. 7720.[3] Only votes with Isabela for congressional representation.
^Died on February 26, 2003.
^Elected to complete the unexpired term of predecessor, assumed office on May 19, 2003.
^Esguerra, Darryl John (27 September 2018). "Duterte creates two new legislative districts in Isabela". newsinfo.inquirer.net.
^. March 4, 2016 https://web.archive.org/web/20160304201114/http://www.congress.gov.ph/download/ra_09/RA07720.pdf. Archived from the original (PDF) on March 4, 2016. {{cite web}}: Missing or empty |title= (help)
^Jernegan, Prescott F. (2009). The Philippine Citizen. BiblioBazaar. p. 80. ISBN 978-1-115-97139-3.