Citizen Science (CS) for nature sensing has gained popularity in recent years. Yet, little is known about the demographics of participants and to what extent they can be classified into specific participant groups. Knowing more about such groups could help attract, engage, and retain CS participants. Therefore, we aimed to identify distinctive participant groups in two ecological CS projects (N1 = 847, N2 = 223) and performed cluster analyses based on participants’ demographic data. The results revealed four clusters in each project: (1) All-Round Workers who were middle-aged, medium-educated, full-time or part-time employees, (2) Academic Employees who were middle-aged, highly educated, full-time or part-time employees, (3) Free-Timers who were medium-educated and non-employed, and (4) Academic Free-Timers who were highly educated and non-employed. Thus, participants of two different ecological CS projects could be classified into similar groups. The grouping of CS participants could, therefore, offer important new opportunities in CS research.