Predation by the lobate ctenophore Mnemiopsis leidyi (hereafter Mnemiopsis) significantly influences marine zooplankton communities in its native and introduced ranges. Although knowledge of detailed spatial and temporal distribution patterns is crucial for understanding Mnemiopsis's population dynamics, many studies are of either relatively short time duration or limited spatial extent. Here, we present monthly data on ctenophore abundance and distribution from the years 2001–07 across 15 stations in Narragansett Bay, Rhode Island, USA. Over these years, ctenophores were first detectable in inshore waters during the spring or summer. Other sites within Narragansett Bay subsequently became populated by Mnemiopsis. As temperatures decreased through the autumn, Mnemiopsis most often had its last seasonal presence also at stations located near the inner margins of the Bay. These data are consistent with previous evidence indicating inshore waters are overwintering sites for Mnemiopsis. High retention regions, such as our stations located in inshore waters, are likely important for long-term establishment of Mnemiopsis populations in temperate waters of both its native and introduced ranges.