In wet temperate regions, human activity has played an important role in shaping the size and distribution of grasslands. We examined change in land cover type and grassland area in a 9.2 × 22.3 km area of northern Chiba Prefecture, based on historical maps and documents for four time periods (1880s, 1950s, 1980s and 2000s). In the 1880s, conifer forests occupied the largest area (43.1%) amongst land cover types and grasslands accounted for 4.2% of the total area. However, literature available from the 1880s suggests that the understorey of conifer forests may have served as additional habitat for grasses. Thus, the habitat of grassland species is suggested to have covered up to 54% of the study area during this time period. By the 1950s, much of the grassland present in the 1880s had been changed to agricultural fields and paddies and grassland area had reduced to 2.9%. Residential development prior to and during the 1980s led to the conversion of forests and agricultural fields to grassland, increasing the grassland area to 11.6% of the study area. Finally, in the 2000s, grasslands had declined to 6.0% of the study area, likely due to conversion to residential areas. Despite these changes over time, 1.5% of the study area has remained as native forest or grassland for over 120 years. The spatial data presented herein are useful for conservation planning and studying the effect of historical land use change on biodiversity.