There is a substantial body of literature concerning evaluation and impact of citizen science (CS) including methodical approaches to measure impact in the best way. However, existing knowledge on the actual outcomes and impact of co- creative citizen social science (CSS) is scarcer. This gap includes how impact in CSS can be measured and assessed in the best way. The H2020 YouCount project can contribute to better understanding of the effects of co-creative CSS as a large multilevel Y-CSS project involving nine countries across Europe and several research substudies. This deliverable introduces the challenges faced when it comes to impact assessment of CSS, the multidisciplinary applied research conducted in YouCount and defines its own approach to impact assessment. The studies’ results show the conclusions of the impact assessment of YouCount, building from the rich variety of the outputs and outcomes produced in YouCount. The study delves into the level of achievement of the intended impact objectives of YouCount; and analyses its unplanned impacts.