  We report the crystal structure of Ba$_2$La$_2$CoTe$_2$O$_{12}$ determined by
Rietveld analysis using X-ray powder diffraction data. It was found from
magnetic measurements that Ba$_2$La$_2$CoTe$_2$O$_{12}$ can be described as a
spin-1\2 triangular-lattice antiferromagnet with easy-plane anisotropy at low
temperatures. This compound undergoes a magnetic phase transition at $T_{\rm
N}\,{=}\,3.26$ K to an ordered state with the $120^{\circ}$ structure. The
magnetization curve exhibits the one-third plateau characteristic of
triangular-lattice quantum antiferromagnets. The antiferromagnetic exchange
interaction and the $g$ factors parallel and perpendicular to the $c$ axis were
evaluated to be $J/k_{\rm B}\,{=}\,22$ K, $g_{\parallel}\,{=}\,3.5$ and
$g_{\perp}\,{=}\,4.5$, respectively.
