Titanium nitride (TiN) is a new plasmonic material with advantages due to its greater thermal and chemical stability, compared to traditional metallic materials, i.e. gold and silver. TiN fabrication methods generally require reactive sputtering, which limits and complicates patterning capabilities. In this work, we demonstrate the fabrication of TiN films, as well as nano-patterned surfaces and three-dimensional (3D) structures by nitridation of crystalline titanium dioxide (TiO₂) nanoparticle-based structures. TiO₂ films are created by spin coating nanoparticle-based solutions, and TiO₂ patterns are fabricated directly via solvent-assisted soft nanoimprint lithography. TiO₂ films and structures were annealed in air and then reacted with ammonia gas at 1000 °C for 0, 2, 4, or 6 hours. SEM analysis shows that patterned TiO₂ surfaces and 3D structures retain their structural integrity after treatment, allowing for a convenient method of fabricating patterned TiN nanopatterned surfaces and structures. Treated samples demonstrate the crystalline transition from tetragonal to cubic, which is consistent with the transition from anatase TiO₂ to TiN. Additionally, using spectroscopic ellipsometry, we observe a change in the real permittivity from positive to negative. For 0 and 6 hour treatments, the real permittivity changes from 3.1 to −9.6 (at 1000 nm). TiN has potential use for many plasmonic and metamaterial applications. In this work, we demonstrate the excitation of surface plasmon polaritons (SPPs) via grating coupling using 1 μm-period TiN line gratings.