This bill enacts "The Tennessee Illegal Immigration Act," which requires a law enforcement agency in custody of an individual known to be unlawfully present in the United States to, as soon as practicable after taking custody of the individual, request an immigration detainer for the individual from the United States immigration and customs enforcement (ICE) division within the United States department of homeland security. IMMIGRATION DETAINER RECEIVED If a law enforcement agency receives an immigration detainer for an individual requested under this bill, then this bill requires the agency to maintain custody of the individual for the maximum period of time specified in the immigration detainer or until the individual is taken into custody by ICE, whichever occurs first. IMMIGRATION DETAINER NOT RECEIVED OR INDIVIDUAL TAKEN INTO FEDERAL CUSTODY BEFORE DETAINER'S EXPIRATION If a law enforcement agency does not receive an immigration detainer requested under this bill before the agency is required to release the individual from custody, or the individual is not taken into federal custody before the expiration of the time period specified in an immigration detainer, then this bill requires the agency to provide transportation to the individual to a city with a sanctuary policy of the individual's choice that is located outside of this state and that is within 700 miles of the law enforcement agency at which the individual is in custody. After transferring the individual, the law enforcement agency must record the actual costs of maintaining custody of the individual and transporting the individual to a city with a sanctuary policy. REPORT OF COSTS – REMITTANCE This bill requires each law enforcement agency to report its actual costs recorded under this bill for each calendar month to the department of revenue no later than the tenth day of each month. For each month subsequent to receiving such reported costs, the department of revenue must (i) request from the United States department of the treasury reimbursement for such reported costs; and (ii) if reimbursement is not received within 30 days of the request, withhold from remittance to the federal highway administration on a month-to-month basis that portion of the federal motor fuel taxes collected in this state equal to the aggregate monthly actual costs reported by law enforcement agencies under this bill. The department must remit monthly to each law enforcement agency that portion of the federal reimbursement or withheld federal motor fuel taxes, as applicable, equal to the agency's monthly reported actual costs for detaining and transporting individuals unlawfully present in the United States.