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The $S1(n,\pi \ast )\leftarrow S0$ cavity ringdown spectrum of 2-cyclohexen-1-one vapor has been recorded in the vicinity of the origin band, which is at $26,089.1\pm 0.1cm-1$. Observation of hot bands in the spectrum has permitted the determination of several low-frequency fundamentals and overtones in the ground electronic state. The lowest two excited quantum states for the inversion vibration, $\nu 39$, were found to be at 99.0 and $197.0cm-1$. Together with previously published far-infrared spectra and vapor-phase Raman spectra, the fundamental frequencies for $\nu 37$ and $\nu 38$ have also been established. From observed $\nu 39$ levels, the barrier to inversion was determined experimentally to be $1900\pm 300cm-1$, which is very different from values of 935 and $3379cm-1$ previously reported from Raman and far-infrared data, respectively. Density functional calculations carried out in the present work give a barrier value of $2090cm-1$ when the $B3LYP/6-311+G(d,p)$ basis set is used.