${\mathrm{CrI}}_2$ is a van der Waals layered material that exhibits helimagnetism that propagates along ribbon chains. This is determined from neutron time-of-flight diffraction measurements. Below $T_N=17$ K in the orthorhombic structure, a screwlike helimagnetic order develops with an incommensurate wave vector of $q\approx (0.2492,0,0)$ at 8 K. Using density functional theory ($\mathrm{DFT})+U$ calculations, the $J_1\text{−}{J}_2$ model is leveraged to describe the helimagnetism, where $J_1(>0)$ and $J_2(<0)$ correspond, respectively, to a ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor intrachain interaction. The $\mathrm{DFT}+U$ calculations suggest that orthorhombic ${\mathrm{CrI}}_2$ satisfies conditions that favor formation of helimagnetic order.