The council seat was left vacant when Mark Allen was elected as the new mayor in January.
Candidates for the seat include Joe Potts, Shari McDaniel, Norma Sanchez Stephens and Jeff McGlothin.
With Cibolo having single-member districts, only residents within District 5 are eligible to vote for the new council member.
The last day to register to vote in the May election is April 6, and the last day to apply for a ballot by mail is April 25. Early voting will occur April 24 through May 2, and election day is May 6.