  Elastic neutron scattering studies of an optimized LaFeAsO single crystal
reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O)
structural transition occurs at $T_\texttt{S} \approx 156$ K, and it exhibits a
sharp transition at $T_\texttt{P} \approx 148$ K. We argue that in the
temperature range $T_\texttt{S}$ to $T_\texttt{P}$, T and O structures may
dynamically coexist possibly due to nematic spin correlations recently proposed
for the iron pnictides, and we attribute $T_\texttt{P}$ to the formation of
long-range O domains from the finite local precursors. The antiferromagnetic
structure emerges at $T_\texttt{N} \approx 140$ K, with the iron moment
direction along the O \emph{a} axis. We extract the iron magnetic form factor
and use the tabulated $\langle j_0\rangle$ of Fe, Fe$^{2+}$ and Fe$^{3+}$ to
obtain a magnetic moment size of $\sim$0.8 $\mu_\texttt{B}$ at 9.5 K.
