Yes. Neutron stars are among the densest objects known, second only to black holes. A typical neutron star packs roughly 1.2 to 2 solar masses into a sphere about 20 km (12 miles) across, so its mean density is about 1014 times that of water—comparable to the density inside an atomic nucleus.
That extreme packing comes from the collapsed core of a massive star: ordinary atomic empty space is crushed away, leaving matter composed mainly of neutrons. Popular comparisons vary, but even a teaspoon of neutron-star material would have an enormous mass by everyday standards.