In United States law, a federal enclave is a parcel of federal property within a state that is under the "Special Maritime and Territorial Jurisdiction of the United States". In 1960, the year of the latest comprehensive inquiry, 7% of federal property had enclave status. Of the land with federal enclave status, 57% (4% of federal property, almost all in Alaska and Hawaii) was under "concurrent" state jurisdiction. The remaining 43% (3% of federal property), on which some state laws do not apply, was scattered almost at random throughout the United States. In 1960, there were about 5,000 enclaves, with about one million people living on them.:146 While a comprehensive inquiry has not been performed since 1960, these statistics are likely much lower today, since many federal enclaves were military bases that have been closed and transferred out of federal ownership.
Since late 1950s, it has been an official federal policy that the states should have full concurrent jurisdiction on all federal enclaves, an approach endorsed by some legal experts.
[Wikipedia: federal enclave; Downloaded 5/9/2021; SOURCE:https://en.wikipedia.org/wiki/Federal_enclave ]
Jurisdiction Over Federal Areas Within the States-Constitution Society Mirror
(2) Determination of presence—
(i) Physical presence.
For purposes of the substantial presence test, an individual shall be treated as present in the United States on any day that he or she is physically present in the United States at any time during the day. (But see §301.7701(b)–3 relating to days of presence that may be excluded.)
(ii) United States.
For purposes of section 7701(b) and the regulations thereunder, the term United States when used in a geographical sense includes the states and the District of Columbia. It also includes the territorial waters of the United States and the seabed and subsoil of those submarine areas which are adjacent to the territorial waters of the United States and over which the United States has exclusive rights, in accordance with international law, with respect to the exploration and exploitation of natural resources. It does not include the possessions and territories of the United States or the air space over the United States.
[26 C.F.R. §301.7701(b)-1(c)(2)]
[EDITORIAL: Notice in paragraph (ii) above the use of the lower case "state" rather than "State" referenced in 26 U.S.C. §7701(a)(10). This means the state is "foreign" in respect to exclusive national government jurisdiction. In the case of an alien, the term "states" includes only federal areas and federal enclaves within the exerior limits of a constitutional state. It does not include land under the exclusive jurisdiciton of a constitutional state as far as we can tell. In the case of those who are "nationals" or "state nationals", the presence test DOES NOT apply because they are not "aliens" and are not privileged. Thus, whether they are "nonresident" is determined by whether they live in the GEOGRAPHICAL "United States" described in 26 U.S.C. §7701(a)(9) and (a)(10) RATHER than "the states and the District of Columbia" as described in paragraph (ii) above.]