A question about the Guano Islands Act
<p>Should I send a letter to a local State Department or the one in DC. I was also wondering if the government will still honor this law?</p>

<p>(U.S. Code Chapter 8 Title 48)</p>

<p>The law has not been repealed. Assuming that the island satisfies the requirements for such a claim, probably the process starts with the Department of State (see <a href="https://www.law.cornell.edu/uscode/text/48/1412" rel="nofollow noreferrer">48 USC 1412</a>), since you must</p>

<blockquote>
  <p>furnish satisfactory evidence to the State Department that such
  island, rock, or key was not, at the time of the discovery thereof, or
  of the taking possession and occupation thereof by the claimants, in
  the possession or occupation of any other government or of the
  citizens of any other government, before the same shall be considered
  as appertaining to the United States.</p>
</blockquote>

<p>If the land is already claimed by the US, for example <a href="https://en.wikipedia.org/wiki/Johnston_Atoll" rel="nofollow noreferrer">Johnson Atoll</a>, then the matter probably goes to the Department of the Interior who will probably say no because it has been deemed a wildlife refuge. It appears that all such islands of the US are reserved as a wildlife refuge or monument of some kind. There do not appear to be any actually unclaimed islands, which is important since the island has to be "not within the lawful jurisdiction of any other government". </p>

<p>Exercise is discretionary. 48 USC s. 1411:</p>

<blockquote>
  <p>[The island] may, at the discretion of the President, be considered as appertaining to the United States.</p>
</blockquote>

united-states