An interesting article on myjourneytomillions.com explores whether handwritten wills are valid, and whether individuals are better off drafting a handwritten will than they are using a do-it-yourself service like legalzoom, or hiring a lawyer.  In Mississippi, a handwritten will, which is called a "holographic will", is legal as long as it is completely in the handwriting of the decedent.  Fill in the blank forms will now serve as a handwritten will.  The problem with handwritten wills comes in presenting them to the court for probate.  Because such wills are not witnessed, the only proof that the document was written and signed by the decedent is testemony, usually by affidavit, of non-experts that they recognize the will as being in the decednet's handwriting. If this is challenged by one of the heirs, this could lead to significant litigation, possible great expense in hiring handwriting experts, and the possible invalidity of the will. Additionally, in all but the simplist of dispositions of property, such as "everything divided equally among my children," the handwritten will is likely to be inadequate to address many of the concerns that a comprehensive estate plan will address, such as protection from divorce, creditors, or nursing home expense. 

In short, yes handwritten wills are valid in Mississippi, but with them comes some risk, and they may be inadequate to deal with the real-life issues of the heirs in all but the simpliest of estates.