Correlation studies between thin film nanostructure and macroscopic magnetic properties in ultrathin fcc Fe films grown epitaxially on room temperature Cu(100) substrates were performedinsituusing an ultrahigh vacuum scanning transmission electron microscope and the surface magneto‐optic Kerr effect. Nanometer lateral spatial resolution secondary electron microscopy revealed no gross morphological changes in the 2–10 monolayer thickness range. The use of broad‐beam Auger electron spectroscopy as an indicator of Cu surface cleanliness is shown to have insufficient sensitivity to detect surface contamination as evidenced by corresponding secondary electron micrographs. Cu(100) surfaces with both (nearly) perfect and imperfect surface structure, and identical Fe coverages, possess nearly identical polar and longitudinal Kerr hysteresis loops. Analysis of reflection high‐energy electron diffraction patterns confirms that Fe films grown on room temperature Cu(100) remain fcc with the same in‐plane lattice constant as the Cu template, for thicknesses up to 10 ML.