Iron-based chalcogenides are complex superconducting systems in which orbitally dependent electronic correlations play an important role. Here, using high-resolution angle-resolved photoemission spectroscopy, we investigate the effect of these electronic correlations outside the nematic phase in the tetragonal phase of superconducting FeSe1−xSx (x=0,0.18,1). With increasing sulfur substitution, the Fermi velocities increase significantly and the band renormalizations are suppressed towards a factor of 1.5–2 for FeS. Furthermore, the chemical pressure leads to an increase in the size of the quasi-two-dimensional Fermi surface, compared with that of FeSe, however, it remains smaller than the predicted one from first-principles calculations for FeS. Our results show that the isoelectronic substitution is an effective way to tune electronic correlations in FeSe1−xSx, being weakened for FeS with a lower superconducting transition temperature. This suggests indirectly that electronic correlations could help to promote higher-Tc superconductivity in FeSe.