  We have analyzed the data from a large-scale CO survey toward the northern
region of the Small Magellanic Cloud (SMC) obtained with the Atacama Compact
Array (ACA) stand-alone mode of ALMA. The primary aim of this study is to
comprehensively understand the behavior of CO as an H$_2$ tracer in a
low-metallicity environment ($Z\sim0.2~Z_{\odot}$). The total number of mosaic
fields is $\sim$8000, which results in a field coverage of 0.26$~$degree$^{2}$
($\sim$2.9 $\times$10$^{5}$$~$pc$^2$), corresponding to $\sim$10$\%$ area of
the galaxy. The sensitive $\sim$2$~$pc resolution observations reveal the
detailed structure of the molecular clouds previously detected in the
single-dish NANTEN survey. We have detected a number of compact CO clouds
within lower H$_2$ column density ($\sim$10$^{20}$$~$cm$^{-2}$) regions whose
angular scale is similar to the ACA beam size. Most of the clouds in this
survey also show peak brightness temperature as low as $<$1$~$K, which for
optically thick CO emission implies an emission size much smaller than the beam
size, leading to beam dilution. The comparison between an available estimation
of the total molecular material traced by thermal dust emission and the present
CO survey demonstrates that more than $\sim$90$\%$ H$_2$ gas cannot be traced
by the low-$J$ CO emission. Our processed data cubes and 2-D images are
publicly available.
