Gilberto Escamilla, 53, arranged for deliveries of the Mexican meal to the Darrell B Hester Juvenile Detention Centre where he worked, but would sell them on himself the same day.
He was caught out last August when he took the day off to go to a medical appointment.
The centre's meat supplier called to confirm an order of 880lbs of fajitas, and the employee who answered informed them the centre doesn't serve the spicy snack.
The supplier had been delivering similar orders for nine years, and officers found stacks of fajitas in Escamilla's fridge.
He was fired and arrested the next day.
He admitted theft by a public servant on Friday and was jailed for 50 years.
Source: Sky News