Simple Summary: The global pest Spodoptera frugiperda (Lepidoptera: Noctuidae) colonized maize in Shizong, Qujing, Yunnan, China in 2019 and caused great economic loss. To monitor this pest and reduce the damage it causes, this study explored the temporal and spatial distribution of S. frugiperda in local fields from 2020 to 2021. The results showed that (1) there were two peaks in the density of eggs, larvae, and adults in both 2020 and 2021 throughout the maize growth period; (2) larvae of all instars were found in all growth stages and in different parts of maize, except 1st instar larva, which did not damage the male ears. However, the relative composition of different instars differed among growth stages and parts of maize; (3) larvae mainly damaged the heart leaf before the tasseling stage and the female ears after the tasseling stage; (4) early instar larvae were aggregated in mountain maize fields, while late instar larvae were distributed uniformly. This study provides monitoring data for S. frugiperda that can function as a guide for predictive models in integrated pest management programs. Spodoptera frugiperda (Lepidoptera: Noctuidae) is a major pest of maize worldwide. This pest colonized maize in Shizong, Qujing, Yunnan, China in 2019. To explore the temporal and spatial distribution of S. frugiperda in local fields, "W" type 5-point sampling was performed from 2020 to 2021. The spatial distribution was analyzed using the aggregation index, Iwao's regression, and Taylor's power law. The temporal distribution showed two peaks for both 2020 and 2021 when the density of eggs, larvae, and adults was high throughout the maize growth period. Additionally, 1st and 3rd instar larvae were higher in number during the maize seedling, jointing, and spinning stages. Fourth to 6th instar larvae were higher in number after the tasseling stage. Additionally, the spatial distribution results showed that 1st to 3rd instar larvae were aggregated, while 4th to 6th instar larvae were uniformly distributed in mountain maize fields. This study provides monitoring data for S. frugiperda and clarifies the temporal and spatial distribution characteristics for larvae in mountain maize fields. Further, it also provides guidance for investigation into population dynamics and the development of predictive models for integrated S. frugiperda management. [ABSTRACT FROM AUTHOR]