  Entropy is a fundamental thermodynamic quantity that is a measure of the
accessible microstates available to a system, with the stability of a system
determined by the magnitude of the total entropy of the system. This is valid
across truly mind boggling length scales - from nanoparticles to galaxies.
However, quantitative measurements of entropy change using calorimetry are
predominantly macroscopic, with direct atomic scale measurements being
exceedingly rare. Here for the first time, we experimentally quantify the polar
configurational entropy (in meV/K) using sub-\r{a}ngstr\"{o}m resolution
aberration corrected scanning transmission electron microscopy. This is
performed in a single crystal of the prototypical ferroelectric
$\mathsf{LiNbO_3}$ through the quantification of the niobium and oxygen atom
column deviations from their paraelectric positions. Significant excursions of
the niobium - oxygen polar displacement away from its symmetry constrained
direction is seen in single domain regions which increases in the proximity of
domain walls. Combined with first principles theory plus mean field effective
Hamiltonian methods, we demonstrate the variability in the polar order
parameter, which is stabilized by an increase in the magnitude of the
configurational entropy. This study presents a powerful tool to quantify
entropy from atomic displacements and demonstrates its dominant role in local
symmetry breaking at finite temperatures in classic, nominally Ising
ferroelectrics.
