The Barbour Collection of Connecticut Town Vital Records says that Levi/Levy Barnum married Joanna Stocker on January* 11, 178[ ] (*July and March crossed out). Thus, the actual date is uncertain. The probable date given in this genealogy is based upon the birth of their first known child, Sabra Stocker Barnum, on 14 January 1782.
Connecticut, Vital Records, Prior to 1850, database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QP74-X4SN : 20 February 2019) gives them a marriage date of "abt January 11, 1780".