If no candidate wins more than 50 percent of the vote, a runoff between the top two vote-getters will be May 14.
The vacancy was created when former Sen. Gloria Negrete McLeod, D-Chino, stepped down to take a seat in the U.S. House of Representatives.
Assemblywoman Norma Torres, D-Pomona, San Bernardino Auditor-Controller Larry Walker, also a Democrat, as well as Pomona Planning Commissioner Kenny Coble said they would seek to succeed Negrete McLeod in the 32nd District.
Ontario Paul Leon and former Rialto state Assemblywoman Wilmer Amina Carter have showed interest in the seat.
The 32nd Senate District includes Pomona, Ontario, Fontana and Rialto.