<p>Land-use change, driven by urbanization, agricultural intensification, and infrastructure development, poses a serious threat to biodiversity, particularly in the tropical and subtropical forest ecosystems. Tropical moist deciduous Sal (<i>Shorea robusta</i>) forests in the lower Western Himalayas, specifically in the foothills and valleys of Uttarakhand, are currently experiencing rapid habitat fragmentation and degradation. This study assessed butterfly diversity across different land uses in Dehradun valley: natural Sal (<i>Shorea robusta</i>) forests, cantonments, agroforestry plantations, and urban blocks for over two years (March 2022–March 2024). Standardized Pollard Walk surveys conducted once per season across 576 transects yielded 74,737 butterfly individuals representing 145 species from six families. Species richness and abundance were higher in cantonments and natural forests, as compared to urban blocks and agroforestry plantations. NMDS ordination and PERMANOVA revealed distinct butterfly assemblages among different land uses, with natural forests and cantonments supporting more specialized and diverse communities. Urban and agroforestry sites exhibited homogenized assemblages dominated by ubiquitous and urban exploiters. Seventeen species recorded in the study area are protected under the Indian Wildlife Protection Act (1972, amendment 2022). Cantonments, functioning as semi-natural green spaces, supported both forest and urban species, underscoring their transitional role in fragmented landscapes. The study highlights the utility of butterflies as bioindicators of natural forest habitats and stresses the urgent need to conserve natural sal forests and integrate biodiversity-supportive practices in land-use planning to mitigate biodiversity loss in the rapidly urbanizing lower western Himalayan sub-region.</p>