Polygamy is common in many taxa, particularly birds. Several hypotheses support evolutionary or ecological explanations for the presence of polygamous mating systems, but these may not explain rare occurrences of polygamy in predominantly monogamous systems. We identified 12 cases of polygyny in 3 populations of varying landscape structure (contiguous wildlands, fragmented wildlands, and suburban) across 97 years of collective study on the monogamous Florida Scrub-Jay (Aphelocoma coerulescens). We categorized each case based on social similarities and compared reproduction between monogamous family groups and polygynous males and females. We found no difference in the relative rate of polygyny across the 3 populations. Neither presence of helpers, annual helper sex ratio, or breeder female survival were associated with polygyny occurrence. Reproductive output was similar between polygynous and monogamous males, but significantly lower for polygynous versus monogamous females. Polygyny in Florida Scrub-Jays appears to occur under certain social contexts but is rare even as those contexts are not. Neither sex appears to benefit from polygynous matings but forming a polygynous triad may be better than forgoing breeding.