The mother, Jessica Darlene White, 3614 Watterson St., Apt. 46, Kingsport, was located in a neighboring apartment, admittedly drinking beer.
Police said White, who turned 20 on Monday, had the smell of alcohol on her breath.
Kingsport police were dispatched to the residence, located in the Hawkins County section of the city, around 4:30 a.m. Sunday.
The child was allegedly found alone by police in the upstairs area of Apt. 50, and Kingsport Police Department Officer Steve Hammonds stated in his report that the stairwell was not protected by a baby gate.
Police also allegedly located a wooden pipe containing what was believed to be burnt marijuana in White's apartment.
White was arrested and charged with child abuse/neglect, underage alcohol consumption and possession of drug paraphernalia.
She was released from the Hawkins County Jail on bond Sunday evening.