Based on first-principles calculations combined with theoretical analysis, we identify a family of monolayer chromium-based group-IV chalcogenides as a new class of two-dimensional (2D) magnetic higher-order topological insulators (HOTIs). Specifically, the $\mathrm{CrC}{X}_3$ ($X=\mathrm{S}$, Se, Te) and ${\mathrm{CrSiS}}_3$ monolayers are found to host conventional antiferromagnetic ground states with $\mathcal{PT}$ symmetry, whereas the Janus compounds ${\mathrm{Cr}}_2{\mathrm{C}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$ and ${\mathrm{Cr}}_2{\mathrm{Si}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$ exhibit altermagnetic ground states. We demonstrate that all these monolayer magnetic materials realize 2D HOTI phases, in which the nontrivial topology is protected by lattice $C_3$ rotational symmetry and manifests as zero-dimensional corner states carrying quantized fractional charges. Moreover, upon inclusion of spin-orbit coupling, these systems remain in the HOTI phase and continue to host robust corner-localized states, confirming the stability of their higher-order topological nature. Our results reveal an intrinsic connection between higher-order topology and magnetic order in 2D antiferromagnetic and altermagnetic systems, identifying chromium-based group-IV chalcogenide monolayers as promising platforms for exploring higher-order topological phases and their potential relevance for future topological and spintronic applications.

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• Electrical properties
• Electronic structure
• Magnetism
• Spintronics
• Symmetry protected topological states
• Topological insulators
• Topological phases of matter
• Topological materials
• First-principles calculations