Microplastics (MP) enter the aquatic environment via several pathways. Many research groups have focused on municipal discharge, while research on industrial sources is rare. This study provides one of the first insights into MP occurrence and distribution in the wastewater systems of industrial parks (IPs) and their wastewater treatment plants (IPWWTPs). The effluents from production plants as well as influent, effluent, and internal samples from the IPWWTPs were assessed. Sampling methods for parallel MP mass and number analyses were developed for varying conditions. The total item emissions of MP (≥10 μm) into the environment were analyzed using μ-Raman spectroscopy and ranged from 3 · 102 to 8 · 104 MP m−3, with a median of 6 · 103 MP m−3 per IPWWTP. Masses analyzed using differential scanning calorimetry showed an MP mass discharge into the environment of 0.2 to 11 mg m−3 with a median of 3.7 mg m−3 per IPWWTP. MP item concentrations within an IPWWTP varied by two to three log levels over several days. Fibers were rare in all samples. Polymer types varied depending on the types of industrial sites and the production plants discharging into the IPWWTP. Within an IP, MP could be allocated to its dischargers, which could be useful for future regulatory requirements. Further research is needed to include different types of IPs producing various polymers and additional processing plants to expand this data set. Display omitted •German industrial parks as MP emitters to the environment were researched in detail.•Detection of mass- and number concentrations with a simultaneous sampling technique•MP deriving from plastic producers is detectable throughout the wastewater system.•Total MP numbers per day within IPWWTPs fluctuate greatly over time.•In- and effluent MP concentrations of industrial and municipal WWTPs are comparable.