  In this work we revisit the phase diagram of Co-doped LaFeAsO using single
crystals and thermodynamic methods. From magnetic susceptibility studies we
track the doping evolution of the antiferromagnetic phase, revealing a
continuous suppression of $T_\mathrm{N}$ up to 5$\%$ Co doping. In order to
study the evolution of the so-called nematic phase, the temperature dependence
of the lengths changes along the $a$ and $b$ orthorhombic directions, $\Delta
L/L_0$, was determined by high-resolution capacitance dilatometry. The results
clearly show a gradual reduction of the orthorhombic distortion $\delta$ and of
$T_\mathrm{S}$ with increasing Co content up to 4.5$\%$, while it is completely
suppressed for 7.5$\%$ Co. Bulk superconductivity was found in a small doping
region around 6$\%$ Co content, while both $T_\mathrm{c}$ and the
superconducting volume fraction rapidly drop in the neighbouring doping regime.
Ultimately, no microscopic coexistence between the superconducting and magnetic
phases can be assessed within our resolution limit, in sharp contrast with
other iron-pnictide families, e.g., electron- and hole-doped BaFe$_2$As$_2$.
