Is all the land in the US owned by someone either private owners businesses or government?

Yes. All the land in the United States is owned by some entity.

In some cases the identity of the legal owner cannot be determined. The reason may be that the land was too difficult to survey at the time of the original surveys. In that case the government would be the owner by default. A more common case occurs when land is in undeveloped or remote areas, the original owner died long ago and the estate was never probated to help establish the chain of title.

In Massachusetts when the present owner cannot be determined the municipality can assess property taxes against "Owner Unknown" and eventually take possession of the land for non-payment of those taxes. The title can be established by a court decree and the land can eventually be sold to a new owner.