What is domicile? The one place the law treats as your permanent home, which decides whose law governs your estate and which state can tax all of your income.
Residence and domicile are different words. You can be a resident of two states at once, because each state defines residency for its own purposes: a driver's licence, in-state tuition, a tax return. Domicile is singular. It is the place you intend to remain and the place you return to, and you have exactly one at a time, from birth until you deliberately replace it.
Replacing it takes two things at once: abandoning the old domicile and establishing a new one. Intent alone does not do it and neither does presence alone, so the test is what a person's facts say. Where the family lives, where the children go to school, which home is larger and furnished, where the cars and the pets are, where the doctor and the bank and the safe deposit box are, and how many days were spent in each state. A declaration of domicile filed with a Nevada county clerk (NRS 41.191) is a dated, sworn statement of intent and useful for that reason, but it is evidence, not proof, and it loses to a calendar that says otherwise.
What turns on the answer is money and paperwork. Your domicile decides where your estate is probated and whose law reads your will, which is why a will drafted in another state should be reviewed by a Nevada attorney after a move. It also decides which state may tax all of your income rather than only the income sourced within it, which is the whole reason a former state examines a departure to Nevada. Where a large income year or a business sale is involved, that examination is a question for a tax professional licensed in both states.
A worked example
A couple moves from California to Henderson in June, buys a house, and keeps the Bay Area home for a daughter finishing school. They take Nevada licences in July and file a declaration of domicile in August, but they spend 190 days of the year at the old house, their doctors and their bank are still there, and the mail follows them west only for the bills. Two years later California asks which state they were domiciled in, and the licence and the declaration are two facts against six.
Moving to Las Vegas, with the figures
Questions people ask
How long does it take to establish domicile in Nevada?
There is no waiting period. Domicile changes the day you are physically here and intend to stay, which is why the paperwork gets done in the first month: the Nevada licence and registration within 30 days, voter registration, and a declaration of domicile with the county clerk all carry dates that fix when the change happened.
Is a declaration of domicile enough to stop my old state taxing me?
No. It is a sworn, dated statement of intent and good evidence, but no other state is bound by it. What decides the question is the pattern of facts: days in each state, where the family and the main home are, and where the ordinary business of a life is conducted.