The unauthorized or undocumented resident immigrant population is defined as all foreign-born non-citizens who are not legal residents. Most unauthorized residents either entered the United States without inspection or were admitted temporarily and stayed past the date they were required to leave.

Unauthorized residents applying for adjustment to lawful permanent resident (LPR) status under the Immigration and Nationality Act (INA) are unauthorized until they have been granted lawful permanent residence (a green card)—even though they may have been authorized to work. Persons who are beneficiaries of Temporary Protected Status (TPS) are not technically unauthorized.

In Mississippi, as in all states, the definition and treatment of unauthorized or undocumented resident immigrants are primarily governed by federal law, specifically the Immigration and Nationality Act (INA). Unauthorized immigrants are those who have entered the United States without proper inspection or have overstayed their visas. While federal law outlines the processes for these individuals to adjust their status to become lawful permanent residents (LPRs), they remain unauthorized until they successfully obtain a green card. It's important to note that while unauthorized immigrants may not have a legal status, some may be granted work authorization or protection from deportation under certain circumstances, such as having Temporary Protected Status (TPS), which is a temporary immigration status provided to nationals of certain countries experiencing problems that make it difficult or unsafe for their nationals to be deported there. However, TPS holders are not considered unauthorized immigrants, although they do not have LPR status. The state of Mississippi does not have specific statutes that redefine or alter the federal definitions of unauthorized immigrant status, and thus follows the federal guidelines as established by the INA and implemented by federal agencies such as U.S. Citizenship and Immigration Services (USCIS).