You might live across more than a few borders in your life or each year. After all, it's often as easy as passing the "Now Entering…" sign over the highway or remembering the second zip code.
Unfortunately, living in several states may not only subject you to the hassles of multiple state income tax filing, but it can be even trickier when it comes to your estate planning.
This issue was explored by Boston CBS in an article titled "How To Protect Your Estate While Living In Two States."
Living in two or more states might result in planning your estate two or more times. It seems everything has to pass muster to each state (or country, if you're that much more worldly). This is especially true for rather fundamental legal instruments like your general power of attorney or medical directive. The requirements for these legal instruments oftentimes vary from one jurisdiction to another.
A good rule of thumb is to have these legal instruments prepared in your state of legal residency (i.e., where you are registered to vote, have your primary mailing address, register your automobiles, etc.) and then have them reviewed by an attorney in any other state where you also spent part of the year. It may be cheap legal "insurance" to have separate documents for use in each respective state, just to be on the safe side.
It is better to know the legal enforceability of your legal instruments before a crisis.
Reference: CBS Boston (October 19, 2012) "How To Protect Your Estate While Living In Two States"