Dataset for article "Pushing the Study of Point Defects in Thin Film Ferrites to Low Temperatures Using In Situ Ellipsometry" published in Adv. Mater. Interfaces 2021, 8, 2001881. The data includes: XRD data of La1-xSrxFeO3 thin films Optical conductivity of LSF films as a function of oxygen partial pressure and Sr content Concentration of electronic holes in LSF thin films as a function of oxygen partial pressure and temperature Defect chemistry models employed for describing the concentration of point defects in LSF thin films. Equilibrium constants for oxygen incorporation reactions in LSF thin films at different temperatures Ellipsometry raw data of LSF50 thin film as a function of equivalent oxygen pressure Electrochemical impedance spectra of the LSF50 thin film at 400 ºC