Long-term management of American Alligator (Alligator mississippiensis) populations necessitates a more detailed understanding of the species' ecology in human-dominated areas. We conducted a 3-yr monitoring program of American Alligators on Jekyll Island, Georgia, USA, to investigate seasonal fluctuations in abundance and the abiotic and biotic (habitat) factors influencing American Alligator abundance in human-made stormwater lagoons. We conducted monthly daytime and evening spotlight surveys from April 2011 to September 2014. Spotlight counts yielded more accurate estimates of abundance. We observed American Alligators using human-made stormwater lagoons throughout the year; however, we observed significantly fewer individuals in the winter season (November–February) than in the mating (March–June) and nesting (July–October) seasons. We collected data on lagoon salinity, lagoon area, percentage of shoreline vegetation, and distance to nearest lagoon. We used the second-order Akaike Information Criterion with a correction for finite sample sizes and subsequent model averaging techniques to examine the relationship between these factors and American Alligator abundance. We found lagoon area to be the most important predictor of abundance relative to the other three independent variables. Salinity was negatively related to American Alligator abundance. Vegetation and distance to nearest lagoon were significant and positively correlated, although ranked lower in our abundance models. Elucidation of these biological trends will allow land managers to better predict when and where human–alligator encounters may occur. In addition, these data may provide developers with valuable information on how to construct stormwater lagoons to promote or discourage lagoon colonization by American Alligators.