The stability, trapping and mobility of electron holes are investigated in lanthanum ferrite LaFeO$_3$ , and in La$_{1−x}$Sr$_x$FeO$_{3−δ}$ ($x$ ≈ 0.1, 0.4 and 0.6) by hybrid-density-functional and densityfunctional-theory $+ U$ calculations. In pure LaFeO$_3$ , the electron hole is more stable under a localized (polaronic) form than under a delocalized form, the energy difference (self-trapping energy) lie between ≈-0.3 and-0.4 eV. This self-trapped hole polaron is not strictly localized on a single Fe atom: instead, it occupies a quantum state made of a 3d orbital of a Fe atom, strongly hybridized with 2$p$ orbitals of four neighboring oxygens. The hole polaron is thus localized on five atoms (among which one single Fe), which can be described as the Fe$^{3+}$ oxidation into Fe$^{4+}$. Electron hole transport results from the combination of onsite reorientations and hoppings, with energy barriers estimated at ≈0.01–0.20 eV and 0.3–0.4 eV, respectively. The aliovalent substitution of lanthanum by strontium in LaFeO$_3$ induces the presence of localized electron holes, preserving the insulating character of La$_{1−x}$Sr$_x$FeO$_3$, regardless of the studied Sr concentration. The formation energy of the oxygen vacancy in La$_{1−x}$Sr$_x$FeO$_3$ (x ≈ 0.1 and 0.4) is estimated at ≈ +0.8 eV. This value is here successfully use to quantify the evolution of defect concentration as a function of the oxygen partial pressure