Elastic neutron-scattering studies of single-crystal LaFeAsO reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O) structural transition occurs at T_S≈156 K, and it exhibits a sharp transition at T_P≈148 K. We argue that in the temperature range T_S to T_P, T and O structures may dynamically coexist possibly due to nematic spin correlations recently proposed for the iron pnictides, and we attribute T_P to the formation of long-range O domains from the finite local precursors. The antiferromagnetic structure emerges at T_N≈140 K, with the iron moment direction along the O a axis. We extract the iron magnetic form factor and use the tabulated ⟨j₀⟩ of Fe, Fe2+, and Fe3+ to obtain a magnetic moment size of ∼0.8 μ_B at 9.5 K.