San Antonio-Castellanos is an urban conurbation the Castellanos Department, in Santa Fe Province in northeastern Argentina. It extends between the localities of San Antonio and Castellanos.
Considered as an urban agglomeration by INDEC since 2001, according to the results of the 2010 census, San Antonio-Castellanos had a population 752 inhabitants, which represented an increase compared to the previous census that had 723 inhabitants.