Federal law (the FLSA) requires an employer to pay final wages by the next regular payday. Many states set a shorter deadline, so check your state.
Final paycheck deadline in the U.S.
What your final pay must include
Your final paycheck must include all the wages you earned through your last day. Whether it also has to include unused vacation depends on your state and your employer's policy, some states treat accrued vacation as wages that must be paid out. See PTO payout rules. If an employer misses the deadline, many states add penalties. This is general information, not legal advice.