  CrI$_3$ is a promising candidate for the van der Waals bonded ferromagnetic
devices since its ferromagnetism can be maintained upon exfoliating of bulk
crystals down to single layer. In this work we studied critical properties of
bulk CrI$_3$ single crystals around the paramagnetic to ferromagnetic phase
transition. Critical exponents $\beta$ = 0.260(4) with a critical temperature
$T_c$ = 60.05(13) K and $\gamma$ = 1.136(6) with $T_c$ = 60.43(4) K are
obtained by the Kouvel-Fisher method, whereas $\delta$ = 5.32(2) is obtained by
a critical isotherm analysis at $T_c$ = 60 K. The critical exponents determined
in bulk CrI$_3$ single crystals suggest a three-dimensional long-range magnetic
coupling with the exchange distance decaying as $J(r)\approx r^{-4.69}$.
