This study presents an updated checklist of angiosperms from the Inhamum Municipal Environmental Protection Area (IMEPA), municipality of Caxias, a strategic area for understanding the Cerrado flora in the State of Maranhão, Brazil. The data presented provides information on the most representative taxa, number of collections, physiognomies of occurrence, life forms, endemicity to Brazil, new records for the State and a floristic similarity analysis with other Cerrado areas in this State. A total of 16 field excursions were carried out from January 2018 to June 2019, with random collections of fertile specimens made mostly on trails. We found 228 species of angiosperms distributed in 148 genera and 50 families. The most representative family was Leguminosae, with 54 species and 33 genera. Cyperus (Cyperaceae) was the most representative genus with seven species. A total of 40 species are endemic to Brazil, and ten are new occurrences for the State of Maranhão. The similarity analysis showed that the composition of angiosperm species from IMEPA is closer to that from the Buriti do Meio Environmental Protection Area, another conservation unit located in the same mesoregion within the State of Maranhão. Nonetheless, low similarity values were recorded, demonstrating an exclusive local richness in the analyzed areas. This study contributed to the knowledge of the Cerrado flora from the State of Maranhão, filling in the Cerrado diversity gaps in Northern Brazil.