Single-walled carbon nanotubes (SWCNTs) are a unique material. The properties of SWCNTs can be modified with covalent and noncovalent functionalization, the substitution of carbon atoms in the SWCNT walls, intercalation, and filling. Filling the SWCNTs can lead to novel materials with modified properties. In this work, we filled the SWCNTs with cobalt chloride and investigated the filled material using different methods to reveal the modification of the electronic properties. First, we investigated the filled SWCNTs with optical absorption spectroscopy (OAS). In the OAS spectra, the characteristic peak of optical transitions between the first van Hove singularities of the semiconducting SWCNTs was suppressed. This corresponded to the Fermi level shift of the SWCNTs. Second, we applied Raman spectroscopy to the cobalt chloride-filled SWCNTs to investigate the changes in the Raman modes of the filled SWCNTs. In the radial breathing mode, shifts in the peaks of D-, G-, and 2D-bands of the cobalt chloride-filled SWCNTs were observed. With three laser wavelengths, the changes in the properties of the semiconducting and metallic-filled SWCNTs were analyzed. The doping of the SWCNTs was subsequently detected. Third, near-edge X-ray absorption fine-structure spectroscopy was applied to reveal and prove the chemical bonding in the cobalt chloride-filled SWCNTs. Fourth, the C 1s X-ray photoelectron spectra of the cobalt chloride-filled SWCNTs were analyzed. The spectra of the filled SWCNTs demonstrated shifts and broadening, which confirmed the p-doping of the SWCNTs. Therefore, all four methods proved the variations in the electronic properties of the cobalt chloride-filled SWCNTs. These results are needed for nanoelectronic applications.