A trust created in an individual’s will, as part of the same document, is called a testamentary trust. Because a will can become effective only upon death, a testamentary trust is generally created at or following the date of the settlor’s death. They do not address the management of your assets during your lifetime. They can, however, provide for young children and others who would need someone to manage their assets after your death.

Since it would take effect at your death it should be included in your Will. If it were made separate, their could be inconsistent provisions and it also would have to be signed with the same requirements as a Will in Mississippi.  So, include it in your Will.