Dendritic cells (DC) in the lung that induce Th17 differentiation remain incompletely understood, in part because conventional CD11b+ DCs (cDC2) are heterogeneous. Here, we report a population of cDCs that rapidly accumulates in lungs of mice following house dust extract inhalation. These cells are Ly-6C+, are developmentally and phenotypically similar to cDC2, and strongly promote Th17 differentiation ex vivo. Single cell RNA-sequencing (scRNA-Seq) of lung cDC2 indicates 5 distinct clusters. Pseudotime analysis of scRNA-Seq data and adoptive transfer experiments with purified cDC2 subpopulations suggest stepwise developmental progression of immature Ly-6C+Ly-6A/E+ cDC2 to mature Ly-6C-CD301b+ lung resident cDC2 lacking Ccr7 expression, which then further mature into CD200+ migratory cDC2 expressing Ccr7. Partially mature Ly-6C+Ly-6A/E-CD301b- cDC2, which express Il1b, promote Th17 differentiation. By contrast, CD200+ mature cDC2 strongly induce Th2, but not Th17, differentiation. Thus, Th17 and Th2 differentiation are promoted by lung cDC2 at distinct stages of maturation.