Carbon is not only an essential element for life but also a key player in climate change. The radiocarbon (14C) analysis using accelerator mass spectrometry (AMS) is a powerful tool not only to understand the carbon cycle but also to track pollutants derived from fossil carbon, which have a distinct radiocarbon isotope ratio (Δ14C). Many studies have reported Δ14C of carbon compounds in streams, rivers, rain, snow, throughfall, fine particulate matter (PM2.5), and wastewater treatment plant effluents in South Korea, which are reviewed in this manuscript. In summary, (1) stream and river carbon in South Korea are largely derived from the chemical weathering of soils and rocks, and organic compounds in plants and soils, strongly influenced by precipitation, wastewater treatment effluents, agricultural land use, soil water, and groundwater. (2) Unprecedentedly high Δ14C of precipitation during winter has been reported, which can directly and indirectly influence stream and river carbon. Although we cannot exclude the possibility of local contamination sources of high Δ14C, the results suggest that stream dissolved organic carbon could be older than previously thought, warranting future studies. (3) The 14C analysis has also been applied to quantify the sources of forest throughfall and PM2.5, providing new insights. The 14C data on a variety of ecosystems will be valuable not only to track the pollutants derived from fossil carbon but also to improve our understanding of climate change and provide solutions.