Microplastics (MPs) are an emerging contaminant of concern in aquatic ecosystems, yet knowledge of their presence in Polish inland waters remains fragmented and limited. This review synthesizes the current state of research on MPs contamination in rivers, lakes, and groundwater in Poland, based on 33 scientific publications. It compiles reported contamination levels in various environments, including bottom sediments, wastewater, snow, tap water, and aquatic organisms, with a critical evaluation of the methodological approaches employed. Reported MPs concentrations in water samples ranged from 0 to 280 MPs/L, whereas in sediments, concentrations reached up to 120,000 MPs/kg, with rivers generally exhibiting higher contamination than lakes. Particular attention is given to sampling, extraction, and identification methods, which substantially influence the comparability and reliability of results. Furthermore, the review highlights key methodological gaps, such as the frequent reliance on visual identification and the lack of standardization across studies. We also present current research trends in Poland, identifying areas of growing interest and notable progress. These findings underscore the urgent need for harmonized methodologies and the establishment of a nationwide monitoring system to ensure robust assessment and management of MPs pollution in Poland’s inland waters.