Ilocos Sur's at-large congressional district

Ilocos Sur's at-large congressional district is an obsolete electoral district that was used for electing members of Philippine national legislatures in Ilocos Sur before 1987.

Ilocos Sur first elected its representatives at-large during the 1898 Philippine legislative election for three seats in the Malolos Congress, the National Assembly of the First Philippine Republic, with an additional seat granted to an appointed delegate. Following the installation of U.S. civil government in 1901 and the reorganization of provinces for the Philippine Assembly, Ilocos Sur was divided into a first, second and third district.

Its third district was eliminated following the separation of Abra in 1917. The provincewide electoral district was re-created ahead of the 1943 Philippine legislative election for a seat in the National Assembly of the Second Philippine Republic, with an additional seat assigned to its provincial governor. The district became inactive again following the restoration of the House of Representatives in 1945 when Ilocos Sur returned to electing its representatives from its two districts.

In the unicameral Batasang Pambansa that replaced the House in 1978, Ilocos Sur was included in the multi-member regional electoral district of Region I (Ilocos Region) for its interim parliament. The district was again utilized in the 1984 Philippine parliamentary election when Ilocos Sur was granted two seats in the regular parliament.

After 1986, Ilocos Sur elected its representatives from its two single-member congressional districts restored under a new constitution.

Representation history
{| class=wikitable ! rowspan=2 | # ! colspan=2 | Term of office ! rowspan=2 | National Assembly ! colspan=4 | Seat A ! colspan=4 | Seat B ! colspan=4 | Seat C ! colspan=4 | Seat D !Start!!End ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history
 * rowspan=2 |
 * rowspan=2 |
 * rowspan=2 |
 * rowspan=2 |
 * - style="height:3em"
 * colspan="24" style="text-align:center;" |
 * colspan="24" style="text-align:center;" |

Ilocos Sur's at-large district for the Malolos Congress
! rowspan=2 | # ! colspan=2 | Term of office ! rowspan=2 | National Assembly ! colspan=4 | Seat A ! colspan=4 | Seat B !Start!!End ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history
 * colspan="24" style="text-align:center;" | District created June 18, 1898.
 * - style="height:3em"
 * style="text-align:center;" | –
 * September 15, 1898
 * March 23, 1901
 * style="text-align:center;" | 1st
 * style="background:;" |
 * Marcelino Crisólogo
 * Independent
 * Appointed.
 * style="background:;" |
 * Mariano Fos
 * Independent
 * Elected in 1898.
 * style="background:;" |
 * Francisco Tongson
 * Independent
 * Elected in 1898.
 * style="background:;" |
 * Ignacio Villamor
 * Independent
 * Elected in 1898.
 * Elected in 1898.
 * style="background:;" |
 * Ignacio Villamor
 * Independent
 * Elected in 1898.
 * Elected in 1898.
 * rowspan=2 |
 * rowspan=2 |
 * - style="height:3em"
 * colspan="14" style="text-align:center;" |
 * colspan="14" style="text-align:center;" |

Ilocos Sur's at-large district for the National Assembly (Second Philippine Republic)
! rowspan=2 | # ! colspan=2 | Term of office ! rowspan=2 | Batasang Pambansa ! colspan=4 | Seat A ! colspan=4 | Seat B !Start!!End ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history ! colspan="2" style="text-align:center;" | Member ! Party ! Electoral history
 * colspan="14" style="text-align:center;" | District re-created September 7, 1943.
 * style="text-align:center;" | –
 * September 25, 1943
 * February 2, 1944
 * style="text-align:center;" | 1st
 * style="background:;" |
 * Fidel Villanueva
 * KALIBAPI
 * Elected in 1943.
 * style="background:;" |
 * Alejandro Quirologico
 * KALIBAPI
 * Appointed as an ex officio member.
 * colspan="14" style="text-align:center;" | District dissolved into Ilocos Sur's 1st and 2nd districts.
 * Alejandro Quirologico
 * KALIBAPI
 * Appointed as an ex officio member.
 * colspan="14" style="text-align:center;" | District dissolved into Ilocos Sur's 1st and 2nd districts.
 * colspan="14" style="text-align:center;" | District dissolved into Ilocos Sur's 1st and 2nd districts.
 * rowspan=2 |
 * rowspan=2 |
 * - style="height:3em"
 * colspan="14" style="text-align:center;" |
 * colspan="14" style="text-align:center;" |

Ilocos Sur's at-large district for the Regular Batasang Pambansa

 * colspan="14" style="text-align:center;" | District re-created February 1, 1984.
 * - style="height:3em"
 * style="text-align:center;" | –
 * July 23, 1984
 * March 25, 1986
 * style="text-align:center;" | 2nd
 * style="background:;" |
 * Salacnib Baterina
 * KBL
 * Elected in 1984.
 * style="background:;" |
 * Eric D. Singson
 * KBL
 * Elected in 1984.
 * colspan="14" style="text-align:center;" | District dissolved into Ilocos Sur's 1st and 2nd districts.
 * }
 * Elected in 1984.
 * colspan="14" style="text-align:center;" | District dissolved into Ilocos Sur's 1st and 2nd districts.
 * }
 * }