Low-dimensional magnetic materials have garnered significant interest due to their unique physical properties and potential applications. Nevertheless, the synthesis of one-dimensional (1D) magnetic materials presents challenges, and the properties of these 1D materials at the single-chain limit have not been well investigated. We here explore experimentally and theoretically 1D CrX₂ (X= Cl, Br, I) magnetic single chains residing within carbon nanotubes. Single chains of CrX₂ are confirmed by the atomic-resolution scanning transmission electron microscopy (STEM) imaging and spectroscopy analysis. Electron energy loss spectroscopy clearly reveals the high-spin state of the Cr atoms within the chain. Notably, we present the first precise measurement and analysis of Cr spin state at the single-chain level, revealing that these spin states can be controlled by the local atomic bonding configuration (CrX₂ versus CrX₃ phases). Density functional theory (DFT) calculations support the structural stability and provide the magnetic and electronic properties of the 1D CrX₂ chains.