  Neutron diffraction and magnetic susceptibility studies of orthorhombic
single crystal {\Ksub} confirm the three dimensional (3D) C-type
antiferromagnetic (AFM) ordering of the Mn$^{2+}$ moments at $T_{\rm N}=305 \pm
3$ K which is slightly higher than that of the parent SrMnSb$_2$ with $T_{\rm
N}=297 \pm 3$ K. Susceptibility measurements of the K-doped and parent crystals
above $T_{\rm N}$ are characteristic of 2D AFM systems. This is consistent with
high temperature neutron diffraction of the parent compound that display
persisting 2D AFM correlations well above $T_{\rm N}$ to at least $\sim 560$ K
with no evidence of a ferromagnetic phase. Analysis of the de Haas van Alphen
magnetic oscillations of the K-doped crystal is consistent with hole doping.
