The Mongolian Plateau (MP) is located in the interior of Eurasia, far from the sea, and is extremely vulnerable to climate change and the deleterious effects of human activity. Land degradation is one of the indicators in the United Nations Sustainable Development Goals and combating it is a major challenge in Mongolia that is located in the core part of MP. Using object-oriented remote sensing interpretation, we obtained the refined land cover data of Mongolia from 1990, 2000, 2010, and 2020 with 30-m resolution. The land cover classification of Mongolia comprises 11 categories, which are forest, meadow steppe, real steppe, desert steppe, barren, sand, desert, ice, water, cropland, and built area. Their overall classification accuracies, corresponding to the year, were 82.26%, 82.77%, 92.34%, and 81.84%. The dataset of this study fills the gaps in high-resolution land cover data in Mongolia.