From cost and management perspectives, the sudden outbreak of COVID-19 and the subsequent countermeasures adversely affected labor-intensive construction companies owing to the restrictive guidelines. Following a systematic literature review, this study developed a theoretical framework to assess the impacts of COVID-19 and its countermeasures on construction sites. Based on a developed framework reflecting abroad cases, we explored the Republic of Korea (ROK) situation. Questionnaires were utilized to detect this impact, and were then analyzed using the relative importance index. Through interviews with site managers in the ROK, combined with text-mining and network analysis, this study aimed to pinpoint effective countermeasures and validate the framework. Results revealed that despite policy changes, construction sites in the ROK were not seriously affected during the COVID-19 pandemic. However, while foreign investment remained steady owing to robust financial contracts, labor shortages and cooperative challenges hindered productivity. Additionally, beyond telecommuting and inspections, changing hygiene regulations prompted the adoption of smart technologies. Further, site managers requested the optimization of worker management and smart systems with governance, hygiene, and quarantine policies. Although impacts from other countries have been studied, the experiences of industries in the ROK remain unanalyzed. In addition, the existing literature has only examined the economic viability of the construction industry; therefore, this study assessed the impacts and countermeasures of COVID-19 from the perspective of managers using a unified theoretical framework.