Microplastics (MP) are found in marine sediments across the globe, but we are just beginning to understand their spatial distribution and assemblages. In this study, we quantified MP in Gulf of Maine, USA sediments. MP were extracted from 20 sediment samples, followed by polymer identification using Raman spectroscopy. We detected 27 polymer types and 1929 MP kg−1 wet sediment, on average. Statistical analyses showed that habitat, hydrodynamics, and station proximity were more important drivers of MP assemblages than land use or sediment characteristics. Stations closer to one another were more similar in their MP assemblages, tidal rivers had higher numbers of unique plastic polymers than open water or embayment stations, and stations closer to shore had higher numbers of MP. There was little evidence of relationships between MP assemblages and land use, sediment texture, total organic carbon, or contaminants. Display omitted •Sediments from the Gulf of Maine were extracted and analyzed for microplastics.•Concomitant site data for each station were analyzed versus MP assemblage.•Habitat, hydrodynamics, and station proximity were important drivers of MP assemblage.•Land use and sediment characteristics had little effect on MP assemblage.•Methods must be less time and labor intensive for feasible largescale monitoring.