Here is an excerpt from the Introduction of the book Primary Education in the Khasi and Jaintia Hills: Its Socio-Cultural Roots and Early History (1993) written by E. Weston Dkhar. Dkhar is a prolific author of several books focusing on Khasi folklore and history.
E. Weston Dkhar says: "Documents and maps indicate that the Khasi territory once extended to the Brahmaputra to the North and the greater part of the Surma Valley to the South. Kamakhya hills, where the Kamakhya temple stands, was known to the Khasis as "U Lum ka Meikha" or "The Grand Aunt's Hillock' (to mark the boundary) and many of the towns in the Kamrup District, Nowgong & District and Sylhet District like Kiew-hati (modern spelling Gauhati or Guwahati) meaning, "to ride on the elephant" or "to begin the journey by riding on elephant": Bordwar, Padwa, Jaintiapur, Shati (Chuttack), Shella-bari (Sylhet) and others were once the principal towns of the Khasis or their chief trading centres. The Lake Shati where the town of Chuttack stands belonged to Ka Shati, the wife of U Khang of Mustoh village, the founder of that village sixteen generations from hence."
The excerpt discusses the borders of Khasi territory that stretched from the Brahmaputra river in the north to the Surma Valley in the south. The Surma River is a major river in Bangladesh, part of the Surma-Meghna River System. It starts when the Barak River (as it is known in Manipur) from Northeast India, divides at the Bangladesh border into the Surma and the Kushiyara rivers.
Nowgong District is what we know as Nagaon District. Sylhet district was established on 3rd January 1782, and until 1878 it was part of Bengal province. In that year, Sylhet was included in the newly created Assam Province, and it remained as part of Assam up to 1947.
It is intriguing to know that Khasi territory was much larger than we know it today. We definitely need to find out more about this! If anyone knows more please feel free to tell us in the comments section 😃😃
Additional source: Wikipedia