Step 1: Identify the Assam Rifles. The Assam Rifles is the oldest paramilitary force in India, with its history dating back to 1835. It is responsible for border security along the Indo-Myanmar border and counter-insurgency operations in Northeast India.
Step 2: Locate its headquarters. The headquarters of the Directorate General of Assam Rifles (DGAR) has been located in Shillong, the capital of Meghalaya, for many decades.
Conclusion: The headquarters is located at Shillong.