The short answer
In most states, a will does not need to be notarized to be legally valid — witnesses, not a notary, make a will valid. What is widely recommended is attaching a notarized self-proving affidavit. It's optional in most places, but it makes the probate process significantly smoother.
Witnesses vs. notary
These do two different jobs. Witnesses observe you sign and attest that you appeared competent and un-coerced — that's what makes the will valid. A notary's role is limited to the self-proving affidavit: a sworn statement that streamlines probate. Notarizing a will without witnesses does not, in most states, make it valid.
A small number of states handle this differently, and some now allow a notarized will as an alternative to witnesses. Your state's page notes which rule applies where you live.
Why bother with the affidavit
Without a self-proving affidavit, when your will is submitted to probate the court may need to locate your witnesses to confirm the signing. Years later, that can be hard — witnesses move, lose touch, or pass away. The affidavit removes that step by proving the signing up front, so it's almost always worth including.
Other documents are different
While wills usually don't require notarization, many financial powers of attorney do, and some healthcare directives can be notarized as an alternative to witnesses. Each document type has its own rules, and they vary by state. Estateur includes the correct signing and notarization instructions for each document in your plan.