Urban forests are crucial to alleviate climate change by reducing the amount of carbon dioxide (CO2) in the atmosphere. Although recent research has mapped the ecosystem service worldwide, most studies have not obtained accurate results owing to the usage of high-cost and low-resolution data. Hence, herein, carbon storage and carbon uptake per capita are quantified and mapped for all administrative districts of the Seoul Metropolitan City through (1) the analysis of tree cover via on-site tree investigation and aerial imagery and (2) geographic information system (GIS) analysis, targeting the Seoul Metropolitan City of South Korea, which has achieved the highest level of development. Results indicate that the total carbon storage and carbon uptake of Seoul are approximately 1459024 t and 147388 t/yr, respectively; the corresponding per unit area values are approximately 24.03 t/ha and 2.43 t/ha/yr, which are lower than those of other cities. In particular, carbon storage and uptake per capita benefits of the urban areas, except for the urban forest areas, are confirmed to show a maximum difference (~20 times) between the regions. This signifies a significant difference between areas in receiving carbon per capita benefits. Finally, we intend to quantify the tree cover and carbon cycle of urban areas of Seoul and map them in order to recognize areas requiring potential planting spaces. This will aid landscape planners and policy makers in establishing plans and policies for urban trees toward alleviating climate change and reducing the amount of fine dust and CO2 concentrations.