Cobalt doped Ni-Zn ferrite nanoparticle (NZFC) were synthesized via citrate auto-ignition method to investigate the structural correlations with microscopic length scale of charge transport in system. Impedance spectroscopy revealed that both grain and grain boundary have combined effect on the conductivity relaxation process. Temperature dependent dc conductivity showed Arrhenius behavior for both grain interiors and grain boundaries. Dielectric relaxation mechanism has been elucidated via Harviliak-Negami (H.N.) formalism. Two characteristic length scales i.e. mean square displacement and spatial extent of the charge carriers inside the system were calculated via standard methods. Microstructural parameters such as bond length, bond angles, bond valence sums (BVS) etc. were estimated by Rietveld refinement of the X-Ray Diffraction (XRD) data. Changes in microstructural parameters followed the same trend as the characteristic length scales with the variation of doping content. Optimum transport properties were observed for 10 mol % of doping which were correlated with electron density plotting and BVS of different samples.