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There is no law that says essentially that a person "cannot be denied entrance to their property." Or rather, there is no law that allows immediate self help, if this is what you seek. So someone in your situation would not be justified in simply traveling through private property (or government land closed off to the public) to enter one's own land.
However, one can go to court to get what is known as an easement. An easement is the right to use a part of another's land for things like egress/ingress, if the land is blocked off from all sides. For example: "it can be implied from necessity. In this situation, an estate has been severed, leaving the dominant estate without a means of access. Before an easement will be implied in this situation, the party who would assert the easement must establish that it is strictly necessary for the enjoyment of the property. Mere convenience, or even reasonable necessity, will not be sufficient if there are alternative routes, even if these alternatives prove more difficult or more expensive. All implied easements are based on the presumed intent of the parties, but this sort is additionally supported by the public policy favoring the productive and beneficial enjoyment of property." Schmidt v. Eger, 289 NW 2d 851 - Mich: Court of Appeals 1980 (internal citations omitted).
However, this is not automatic. Someone in your situation would have to go to Court and file something called a QUIET TITLE action, asking the Court to agree to render an easement via a judgment. (Or, a neighbor can agree to provide an easement voluntarily, to avoid litigation.)
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