The magnetic phase diagram of Cr(dien)$({\mathrm{O}}_{2}{)}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{H}}_{2}\mathrm{O}(\text{dien}={\mathrm{C}}_{4}{\mathrm{H}}_{13}{\mathrm{N}}_{3})$, a quasi-two-dimensional spin-1 antiferromagnet known to exhibit quantum phase behavior, is reported. Specific heat, torque magnetometry, and magnetocalorimetry were employed to obtain the phase diagram down to 200 mK. Near the $T\ensuremath{\rightarrow}0$ limit, the antiferromagnetic phase defers to a field-induced ferromagnetic phase at a critical field ${H}_{C}$. Analysis of the phase boundary through fitting with $\left(H\ensuremath{-}{H}_{C}\right)=\ensuremath{\beta}{T}^{\ensuremath{\alpha}}$ yielded ${H}_{C}$ and the critical exponent $\ensuremath{\alpha}$ of the spin system. ${H}_{C}$ and $\ensuremath{\alpha}$ were found to be $15.2\ifmmode\pm\else\textpm\fi{}0.02$ T and $2.05\ifmmode\pm\else\textpm\fi{}0.09$, respectively, when $\mathbit{H}$ is parallel to the easy magnetic axis, and $12.4\ifmmode\pm\else\textpm\fi{}0.01$ T and $1.91\ifmmode\pm\else\textpm\fi{}0.06$ when perpendicular to it. These critical exponents are indicative of an Ising-type spin system, which was an unanticipated result. Furthermore, torque magnetometry detected a spin-flop transition over a wide orientation range of nearly 70\ifmmode^\circ\else\textdegree\fi{} in the $ab$ plane. Mean field theory yielded an estimate of the long sought-after single-ion anisotropy for this compound, $D\ensuremath{\approx}0.25$ K.