The formation and evolution of multiple systems has a significant impact on our understanding of star formation processes and the ability to form planets. Previous multiplicity studies of the Galactic field have shown that the mass ratios and separations of the companion population highly depend on primary mass, while other studies in low-density star-forming regions (e.g. Taurus and Upper Scorpius) uncover a significant excess of companions relative to the field population. In this talk, I will discuss our investigations into the close (< 10 AU) companion population to intermediate mass field stars, where past surveys to date are incomplete, using long-baseline interferometry with MIRC-X at the CHARA Array. I will also detail our study into the role of birth environment on the formation of multiple systems for primary masses = 0.012 - 0.7 Msun and separations down to 0.025" using archival Hubble Space Telescope (HST) data in the Orion Nebula Cluster (ONC), a high-mass high-density star-forming region. Over the course of these two surveys, we have found dozens of companions and placed important constraints on the companion population based on the star-forming region environment and primary mass.