Abstract In order to shed light on how galactic properties depend on the intergalactic medium (IGM) environment traced by the Lyα forest, we observationally investigate the IGM–galaxy connection using the publicly available 3D IGM tomography data (CLAMATO) and several galaxy catalogs in the COSMOS field. We measure the cross-correlation function (CCF) for 570 galaxies with spec-z measurements and detect a correlation with the IGM up to 50 h ⁻¹ comoving Mpc. We show that galaxies with stellar masses of 10⁹−10¹⁰ M _⊙ are the dominant contributor to the total CCF signal. We also investigate CCFs for several galaxy populations: Lyα emitters (LAEs), Hα emitters (HAEs), [O iii] emitters (O3Es), active galactic nuclei (AGNs), and submillimeter galaxies (SMGs), and we detect the highest signal in AGNs and SMGs at large scales (r ≥ 5 h ⁻¹ Mpc), but in LAEs at small scales (r < 5 h ⁻¹ Mpc). We find that they live in various IGM environments—HAEs trace the IGM in a similar manner to the continuum-selected galaxies, but LAEs and O3Es tend to reside in higher-density regions. Additionally, LAEs’ CCF is flat up to r ∼ 3 h ⁻¹ Mpc, indicating that they tend to avoid the highest-density regions. For AGNs and SMGs, the CCF peak at r = 5−6 h ⁻¹ Mpc implies that they tend to be in locally lower-density regions. We suspect that it is due to the photoionization of IGM H i by AGNs, i.e., the proximity effect.