  Measurements of the single photoionization cross section of Cu-like Zn$^+$
ions are reported in the energy (wavelength) range 17.5 eV (709 \AA) to 90 eV
(138 \AA). The measurements on this {\it trans}-Fe element were performed at
the Advanced Light Source synchrotron radiation facility in Berkeley,
California at a photon energy resolution of 17 meV using the photon-ion
merged-beams end-station. Below 30 eV the spectrum is dominated by excitation
autoionizing resonance states. The experimental results are compared with
large-scale photoionization cross-section calculations performed using a
Dirac-Coulomb $R$-matrix approximation. Comparison are made with previous
experimental studies, resonance states are identified and contributions from
metastable states of Zn$^+$ determined.
