Missouri Revised Statutes Title IX. Suffrage and Elections § 115.151. Registration complete, when

1. Each qualified applicant who appears before the election authority shall be deemed registered as of the time the applicant's completed, signed and sworn registration application is witnessed by the election authority or deputy registration official.

2. Each applicant who registers by mail shall be deemed to be registered as of the date the application is postmarked, if such application is accepted and not rejected by the election authority and the verification notice required pursuant to section 115.155 is not returned as undeliverable by the postal service.

3. Each applicant who registers at a voter registration agency or the division of motor vehicle and drivers licensing of the department of revenue shall be deemed to be registered as of the date the application is signed by the applicant, if such application is accepted and not rejected by the election authority and the verification notice required pursuant to section 115.155 is not returned as undeliverable by the postal service. Voter registration agencies shall transmit voter registration application forms to the appropriate election authority not later than five business days after the form is completed by the applicant. The division of motor vehicle and drivers licensing of the department of revenue shall transmit voter registration application forms to the appropriate election authority not later than three business days after the form is completed by the applicant.