The structure and energetics of three CoHNO+ isomers [HCo(NO)(+) (1), Co(HNO)(+) (2), Co(NOH)(+) (3)] were probed by using density functional theory (DFT). Theory predicts that 2 is the most stable structure with 1 and 3 14.1 and 15.4 kcal/mol less stable. We were unable to locate the transition states for 2 --> 1 and 2 --> 3 conversions. DFT calculations predict D-o(CoH+-NO) = 34.6 kcal/mol and D-o(Co+-HNO) = 45.5 kcal/mol. The gas-phase ion chemistry of CoHNO+ was also studied by using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. CID and SORI-CID of CoHNO+ yield competitive formation of Co+, CoH+, and CoNO+. These results suggest that the barrier for 2 --> 1 conversion is less than 45.5 kcal/mol. Reactions with simple molecules were dominated by NO and HNO displacements. Potential energy surface diagrams are presented to explain these displacement reactions. Surprisingly, CoHNO+ reacts with methane by dehydrogenation to yield CoCH3NO+. Studies suggest CH3CoNO+ rather than Co(CH3NO)(+) as the structure for this ion.