We present optical photometry and spectroscopy of the Type IIP supernova SN 2004et that occurred in the nearby galaxy NGC 6946. The observations span a time range of 8541 d after explosion. The late time bolometric luminosity and the H{alpha} luminosity in the nebular phase indicate that 0.06+/-0.02M_{sun} of ^56^Ni was synthesized during the explosion. The plateau luminosity, its duration and the expansion velocity of the supernova at the middle of the plateau indicate an explosion energy of E_exp=1.20^+0.38^-0.30_x10^51^erg. The late time light curve and the evolution of the [OI] and H{alpha} emission-line profiles indicate the possibility of an early dust formation in the supernova ejecta. The luminosity of [OI] 6300, 6364{AA} doublet, before the dust formation phase, is found to be comparable to that of SN 1987A at similar epochs, implying an oxygen mass in the range 1.52M{sun}, and a main-sequence mass of 20M{sun}_ for the progenitor.