The majority of unmarried people in the United States do not have an estate plan in place. This is a disturbing statistic because in fact all responsible adults should execute the appropriate estate planning documents.
If you were to pass away without a last will or any other type of legally binding document directing the transfer of your assets the probate court would take over your affairs. Ultimately your assets would be passed along to relatives along intestacy rules of succession if you do indeed have living family members.
It is very likely that you would want your remaining resources to be distributed in a more precise manner. After all, you may have close friends and extended family that you care about a great deal. Aside from financial resources there are also sentimental items that could mean a lot to the various people that were close to you.
Another thing to consider is the possibility of incapacity. If you were to become incapacitated the state would be forced to appoint a guardian or conservator to handle your affairs if you failed to plan ahead for this possibility.
The preferred course of action would be to execute durable powers of attorney naming representatives of your own choosing to act in your behalf should it become necessary.
There is also the matter of a living will elucidating your preferences with regard to medical procedures such as the utilization of artificial life support measures if you were to fall into an irreversible terminal condition.
The bottom line is this: Estate planning is one of the core responsibilities of adulthood, and single people are not excused.