Background Emerging evidence has underscored infiltrating immune cells in the tumor microenvironment (TME) of non-small cell lung cancer (NSCLC). Owing to screening programs, the prevalence of early-stage NSCLC is growing, but its high recurrence risk and poor survival impose an increasing demand for further understanding the TME. Methods Tissue and plasma samples from 33 resectable stage IA NSCLC patients were collected from the surgery and subject to histological and genomic analyses. The distribution of CD8+ T cells, tumor-associated macrophages (TAMs, M1 polarization and M2 polarization), and natural killer (NK) cells (CD56dim and CD56bright) was analyzed. The impact of clinical characteristics and immunotherapy-related biomarkers on immune cell infiltration were also investigated. Results Using multiplex immunohistochemistry (mIHC), we found a significantly higher M1 polarization proportion of total TAMs in tumor parenchyma than in other tissues, while other immune cells remained stable. Patients under 50 showed higher infiltrating CD8+ T cell density and M1 ratio in tumor tissues. Tumors carrying RAS-MAPK mutations were associated with significantly increased infiltration of CD8+ T cells. We also identified significantly higher infiltration of CD8+ T cells and enrichment of CD56bright NK cells in high tumor mutation burden (TMB) and high programmed cell death ligand 1 (PD-L1) samples, respectively. Conclusions Our study highlighted the heterogeneity and dynamics of infiltrating immune cells in stage IA NSCLC TME, featured by M1 TAM enrichment in tumor parenchyma. Age, driver mutation type, TMB, and PD-L1 level were found to associate with immune cell infiltration in the TME, shedding light on immunotherapy development.