The FTIR and structural properties in co-precipitated cobalt ferrite ($CoFe_2O_4$) nanoparticles are discussed in this paper. The synthesis was conducted at temperatures of $75^\circ C$ and $95^\circ C$ following post annealing at $1200^\circ C$ for 5 hours. Other modification samples were synthesized at temperature of $95^\circ C$ and then annealing at temperature of $1000^\circ C$ and $1200^\circ C$ for 5 hours. For both modification of synthesis and annealing temperature, FTIR result showed a metal oxide at a wave number of $590\ cm^{-1}$ which indicated cobalt ferrite nanoparticles. The crystalline structure was confirmed using X-ray diffraction that the high purity of cobalt ferrite was realized. Calculation of the cation distribution by using comparison $I_{220}/I_{222}$ and $I_{422}/I_{222}$ show that the synthesis and annealing temperature successfully modify cation occupy the site octahedral and tetrahedral.