A 3.34-m plane-grating spectrograph has been used to measure the wavelengths of 11 lines of singly ionized $^{198}\mathrm{Hg}$ emitted by an electrodeless discharge lamp in the region 1942--7944 A\r{}. The uncertainty varies from \ifmmode\pm\else\textpm\fi{}0.0003 to \ifmmode\pm\else\textpm\fi{}0.0015 A\r{}. From these wavelengths, accurate values were determined for all levels of the 5${d}^{10}$6s, 6p, 6d, 7s, 7p, and 5${d}^{9}$6${s}^{2}$ configurations and for four levels of the 5${d}^{9}$6s6p configuration. By using existing isotope-shift data, values of wavelengths and energy levels for natural Hg ii were deduced. Accurate values for 12 lines of Hg ii in the region 893--2026 A\r{} were calculated from the energy levels.