Aim: The importance of SMEs for the Polish economy, their financial condition, and the rules of allocating EU funds to beneficiaries raise the question of the effects of SMEs’ participation in the EU regional policy support. As the matter has not been investigated from the financial perspective of 2014–2020 so far, the study aims to fill this gap. Method: The database included 5679 investments carried out by SMEs located in Mazovian Voivodeship, Poland. The qualitative data included inter alia, information on the main beneficiary type, the exact location and title of the project, the name of the operational program, and its priority and action. Quantitative data included the total value of the investment as well as the value of qualified costs and EU funding. Standard qualitative data analysis (QDA) was applied to analyze the textual information of the entries, while descriptive statistics and comparative analysis were used to make conclusions based on the quantitative data. Results: SMEs in Mazovian Voivodeship (Poland) were very active beneficiaries of operational programs in 2014–2020, which is confirmed by the main financial and quantitative effects of their investment activity. As of March 31, 2023, the total value generated in projects by micro, small, and medium-sized enterprises equaled 10.5 billion PLN. The SMEs’ investments covered a wide range of topics, supporting both the development of enterprises themselves and, at the same time, the social, economic, and environmental development at the local and regional levels. However, some of the actions under operational programs supported this sector during COVID-19 to enable its survival and further functioning. Conclusions: All three subcategories of SMEs, i.e., micro, small, and medium-sized enterprises in Mazovian Voivodeship, benefitted from the EU support, carrying out projects of different values, scopes and thematic profiles, irrespective of their legal form.