Objective: SKG mice develop interstitial lung disease (ILD) resembling rheumatoid arthritis–associated ILD in humans. The aim of this study was to clarify the mechanism underlying the lung pathology by analyzing lung‐infiltrating cells in SKG mice with ILD. Methods: We assessed the severity of zymosan A (ZyA)–induced ILD in SKG mice histologically, and we examined lung‐infiltrating cells by flow cytometry. Total lung cells and isolated monocytic myeloid‐derived suppressor cells (MDSCs) were cultured in vitro with granulocyte–macrophage colony‐stimulating factor (GM‐CSF) and interleukin‐4. The proliferation of 5,6‐carboxyfluorescein diacetate N‐succinimidyl ester–labeled naive T cells cocultured with isolated CD11b+Gr‐1dim cells and MDSCs was evaluated by flow cytometry. CD11b+Gr‐1dim cells were adoptively transferred to ZyA‐treated SKG mice. Results: MDSCs, Th17 cells, and group 1 and 3 innate lymphoid cells (ILC1s and ILC3s) were increased in the lungs; the proportion of these cells varied with ILD severity. In this process, we found that a unique cell population, CD11b+Gr‐1dim cells, was expanded in the severely inflamed lungs. Approximately half of the CD11b+Gr‐1dim cells expressed CD11c. CD11b+Gr‐1dim cells were induced from monocytic MDSCs with GM‐CSF in vitro and were considered tolerogenic because they suppressed T cell proliferation. These CD11b+Gr‐1dim cells have never been described previously, and we termed them CD11b+Gr‐1dim tolerogenic dendritic cell (DC)–like cells. Th17 cells, ILC1s, and ILC3s in the inflamed lung produced GM‐CSF, which may have expanded CD11b+Gr‐1dim tolerogenic DC–like cells in vivo. Furthermore, adoptive transfer of CD11b+Gr‐1dim tolerogenic DC–like cells significantly suppressed progression of ILD in SKG mice. Conclusion: We identified unique suppressive myeloid cells that were differentiated from monocytic MDSCs in SKG mice with ILD, and we termed them CD11b+Gr‐1dim tolerogenic DC–like cells.