Trees outside forests (TOF) are integral components of rural livelihoods providing fodder, fruit, firewood, timber, and other ecosystem services. The extent and magnitude of the contribution of TOF may vary with the different socioeconomic and demographic factors of the households (HHs) within a community. Based on a comprehensive survey of 78 HHs and an inventory of their farms in the Tanahun district, Nepal, this study assessed the species diversity, richness, and carbon storage in TOF in various socioeconomic strata. We found 623 individual trees representing 38 species and 21 families. Species diversity was the highest in the farmland owned by indigenous people according to caste, middle-income class according to the well-being class, and farmers according to the main occupation of the HH. Species diversity varied significantly with the amount of land, the number of livestock, and the distance from one's home to forests; furthermore, the carbon stock per HH varied significantly with the amount of land, the number of livestock, caste, and well-being class. TOF contribute to a national carbon budget and therefore need to be considered in nationally determined contributions and performance-based payments in forestry systems (REDD+). Efforts to regularly measure and monitor TOF by including them in the national forest inventory system are crucial to record their contributions to the overall livelihood of local people and the national carbon budget.