[3] The district consists of the provincial capital city of Malolos and adjacent municipalities of Bulakan (Bulacan), Calumpit, Hagonoy, Paombong and Pulilan.

[4][5] Until its second dissolution in 1972, it also consisted of Balagtas, Bustos, Guiguinto (formerly Bigaa), and Plaridel (formerly Quingua).

The ballots were originally printed with Malolos having a different set of candidates from the rest of the 1st district.

Victoria Sy-Alvarado with an overwhelming lead over Governor Roberto Pagdanganan in the 1st district, and Danilo Domingo also having a majority of the vote in Malolos.

The COMELEC later on ruled that the candidates that were listed in Malolos and the rest of the 1st district shall contest the election.