This dataset describes the quantity, morphology, and polymer identity of microplastics in the water column and surficial sediments of Milwaukee-Area streams, the Milwaukee Harbor, and Lake Michigan (Wisconsin). Water samples were collected at 10 locations, 2-4 times each, from May to September, 2016. At the 4 shallowest locations, water was collected only at the water surface. At the remaining 6 locations, water was collected at the water surface and at 1-4 depths below the surface. Sediment samples were collected once, in June 2016, at a subset of 9 locations. Sampling and analysis methods are described in the Processing Steps section of the metadata. These data are interpreted in the following journal article: Lenaker, P. L., Baldwin, A. K., Corsi, S. R., Mason, S. A., Reneau, P. C., & Scott, J. W. (2019). Vertical Distribution of Microplastics in the Water Column and Surficial Sediment from the Milwaukee River Basin to Lake Michigan. Environmental Science & Technology, 53(21), 12227–12237, https://doi.org/10.1021/acs.est.9b03850.