The paper aims to assess the interaction of environmental indicators with both residents’ health and sustainability in the Slovak Republic, applying the prism of the Smart City Index environment pillar. In this research, data from several districts during the period 2019–2022 will be used with regard to sunshine hours, the share of green space, the level of particulate matter, cases of chronic respiratory diseases, and public participation in nature protection. Some of the main results have been the proof of a direct correlation between green space share and sunshine hours with respect to high-deity particles and chronic respiratory diseases. While there are two ways of trend analysis, improvement in air quality is contrasted by rising health problems. It, therefore, highlights the necessity of targeted interventions and smart city technologies to improve urban sustainability and public health. Among the recommended actions are the provision of more green spaces, essentially enhanced air quality monitoring, the creation of public awareness, and putting in place control measures against pollution.