Socio-ecological theory asserts that mating strategies are dictated by the distribution of females and the ability of males to monopolize them. Within several bottlenose dolphin (Tursiops truncatus) populations, males demonstrate a relatively rare mating strategy: cooperative mate guarding within alliances. Dolphin alliances vary in complexity, but to date, documentation of multi-level alliances has been limited to Shark Bay, Australia. Given the rarity of male reproductive alliances, opportunity for comparative study is limited. This study is the 1st documentation of the complexity of male dolphin alliances in estuarine waters along the Atlantic coast of the United States. Photo-identification data were collected from March 2011 to 2014 in the St. Johns River (SJR) in Jacksonville, Florida. Analyses included individuals sighted 10+ times and were divided into females (n = 78), males (n = 25), and unknown sex (n = 78). Thirty individuals met the criteria for alliance status and 20 individuals formed 2nd-order alliances. Results fit the sex-specific association patterns described for other populations, with low-moderate bonds (half-weight indices) between females and markedly stronger bonds among males and individuals of unknown sex. Comparative studies between the SJR and Shark Bay, Australia, as well as with nearby and ecologically similar field sites are needed to determine the selective pressures (ecological and demographic) shaping alliance complexity.