If my mother just passed andI wasn’t even mentioned in the Will, is that legal?

A parent may disinherit their child. Children typically have no automatic rights of inheritance from a parent. However, as a general rule in such cases, there should be specific disinheritance language in the Will since most states do have laws to protect against an accidental disinheritance. For example, if it appears the parent did not know about a child or if the child was born after the Will was signed. In such cases a child may have a right to “elect against the Will”; that is they have a right to certain assets.  Otherwise, if there is a Will and you're not in it, you are not entitled to anything.

You should be aware that some assets can be transferred outside of probate. For example, if your mother had a small estate, property may have been transferred by affidavit or other small estate procedure. Additionally, some assets may have been held as "joint tenants with right of survivorship", in which case the other joint tenant would have received your mother's share to property operation of law.  In addition, funds in an IRA, pension, 401(k), or other retirement plan bypass probate and go directly to named beneficiaries (unless the beneficiary named was his estate). The same holds true for any life insurance proceeds (and as to such proceeds, unless you were a named beneficiary. You may then want to check as to all of this as well.