What is the legal requirement to be considered a resident of the US Virgin Islands (St. Croix)?
A Legal resident for what purpose? For Voter registration 90 day's, on the island and named on a lease or deed, for tax purpose 6 months of living on the island with lease or deed( this changed due to Hedge fund requirements) the tax authority, call it a bonafide resident. Having a drivers license does not make you a resident, it just allows you to drive on the island, your stateside license is good for up to 90 days.
This is what the IRS says:
Under the new Section 937 an individual is generally considered a bona fide resident of a possession if (1) he or she is physically present in the possession for 183 days during the taxable year, (2) does not have a tax home outside the possession during the tax year, and (3) does not have a closer connection to the U.S. or a foreign country. However, U.S. citizens and resident aliens are permitted certain exceptions to the 183-day rule.
Tax wise there can be advantages to becoming a VI resident.