The 2-cyclohexen-l-one (2CHO) molecule serves as a prototype for understanding the photochemical properties of conjugated enones. We have recorded the cavity ringdown (CRD) absorption spectrum of 2CHO vapor at room temperature over the 360-380 nm range. This portion of the spectrum encompasses the S-1(n,pi*) <- S-0 vibronic band system in the region of the C=C and C=O stretch fundamentals. We have assigned about 40 vibronically resolved features in the spectrum, affording fundamental frequencies for 7 different vibrational modes in the S-1(n,pi*) state, including the C=C (1554 cm(-1)) and OC-CH (1449 cm(-1)) stretch modes. The C=O stretch character is spread over at least four different vibrational modes in the S-1(n,pi*) state, with fundamentals spanning the 1340-1430 cm(-1) interval. This finding stems from a significant reduction in C=O bond order upon excitation, which leads to near-coincidence of the C=O stretch and several CH, wag frequencies. Such complexities make 2CHO an ideal candidate for testing excited-state computational methods. We have used the present spectroscopic results to test EOM-EE-CCSD harmonic-frequency predictions for the S-1(n,pi*) state. We have also benchmarked the performance, of less costly computational methods, including CIS(D) and TDDFT. For certain density functionals (e.g., B3LYP and PBE0); we find that the accuracy of TDDFT frequency predictions can approach but not meet that of EOM-EE-CCSD.