  Using the Kreuzer-Skarke database of 4-dimensional reflexive polytopes, we
systematically constructed a new database of orientifold Calabi-Yau threefolds
with $h^{1,1}(X) \leq 12$. Our approach involved non-trivial $\mathbb{Z}_2$
involutions, incorporating both divisor exchanges and multi-divisor reflections
acting on the Calabi-Yau threefolds. Each proper involution results in an
orientifold Calabi-Yau threefolds and we constructed 320,386,067 such examples.
We developed a novel algorithm that significantly reduces the complexity of
determining all the fixed loci under the involutions, and clarifies the types
of O-planes. Our results show that under proper involutions, the majority of
cases end up with O3/O7-plane systems, and most of these further admit a naive
Type IIB string vacua. Additionally, a new type of free action was determined.
We also computed the smoothness and the splitting of Hodge numbers in the
$\mathbb{Z}_2$-orbifold limit for these orientifold Calabi-Yau threefolds.
