Korean historical chronicles provide a two-thousand-year observational record of natural phenomena, including astronomical and meteorological events. In this paper, we use their records of sunspots and frost to examine the correlation of between solar activity and climate change in Korea. In total, we have 42 sunspot records for the Goryeo Dynasty (AD 918–1392) and 13 for the Joseon Dynasty (AD 1392–1910). Those for the Goryeo Dynasty show a periodicity in good agreement with the well-known 11-year cycle of solar activity, and those for the Joseon Dynasty suggest that solar activity decreased over the following ~500 years. In order to examine the long-period variation of solar activity, we supplement our data with Chinese sunspot records from the same period, and we find a new ~240-yr period of solar activity via power spectral analysis. The Korean chronicles also contain ~700 frost records spanning the last thousand years, and we investigate these records for signs of cooling indicative of climate change. These records point to a ~240-yr cooling period, which is well in accord with that of solar activity. From this, we argue that solar activity has decreased over the last one thousand years and has a long-term variation of ~240 years.