Two-dimensional (2D) van der Waals (vdW) antiferromagnets are promising platforms for exploring quantum magnetism and spintronic devices. However, detecting antiferromagnetic order in ultrathin vdW layers presents a significant technological challenge. This study demonstrates the resolution of in-plane antiferromagnetic order and spin orientation in the atomically thin vdW antiferromagnet CrCl using the resonant magneto-optical Voigt effect. Notably, a pronounced quadratic magnetic linear dichroism is observed at resonant excitonic transitions of around 1.81 eV. Furthermore, we elucidate the antiferromagnetic domains and spin-flop transitions in this system by analyzing both the amplitude and orientation of the magnetic linear dichroism. Our approach leveraging resonant magneto-optical measurements provides an accessible and noninvasive means to probe antiferromagnetic orders and spin dynamics in quasi-2D magnetic systems.