That same year, his son, William McKell, graduated from college, established his residency in Glen Jean, and assumed the office of Treasurer of his father's company. McKell's creation of his company was necessary in the year 1893, as this was the year that coal was first being mined from his properties under lease to various coal companies. Under agreements with the lease holders and the C&O Railway, McKell was paid royalties on the coal mined and sold from his leased lands.

It is true however, that T. G. McKell did not begin operating his own coal mining operations until the early 1900's, opening his first mine at Derry Hale in 1900, followed by the Kilsyth mine in 1901, Oswald in 1903, and the mine at Graham in 1903. Following T. G. McKell's death, on September 22, 1904, the McKell heirs opened the mine at Tamroy in 1907 and the Siltix mine in 1924. In addition, the following mines were also opened on lands leases from McKell: Laura in 1903; Nichol in 1905; Dun Glen in 1905; Newlyn in 1904; and Meadow Fork in 1904. In the years that followed, additional leases were opened on McKell's lands at Dewitt, Calloway, Lee, Cadle Ridge, Sunset, Cepece, Hill Top, Balwood, and Fay-Ral. To obtain a better concept of the location of the McKell mines and leases, see the topic, 1925 Map of the Area's Coal Mines.

The size and importance of the McKell Coal & Coke Company has typically been underestimated by many contemporary historians. This is apparent due, at least in part, because the most easily available source of information on the areas coal mines, History of Fayette County, provides an rather incomplete view of the McKell coal operations. This is due to no fault by the book's authors. The book only contains information on mines operated by the McKell enterprises actually located in Fayette County, simply because it written as a book on Fayette County history. Because McKell's Tamroy, Oswald and Graham mines were actually located in Raleigh County, no mention of these mining operations, nor production figures for them are listed in the History of Fayette County.

In reality, the profits realized by McKell coal empire was very great. McKell received royalty payments for coal mined over the course of many decades from several of the large New River Company mining operations, including the Dunn Loop mines, Turkey Knob, the Collins mine at Glen Jean. In addition, McKell received royalties from coal mined by various other coal operations, including: the Dun Glen, Newlyn, Meadow Fork, DeWitt, Calloway, Lee, Cadle Ridge, Sunset, Cepece, Hill Top, Balwood, and Fay-Ral mines. In addition to making money from off the coal actually being mined by other operators, McKell realized additional profits by hauling the coal produced by many of those operators, via the McKell-owned KGJ&E Railway.

As the mining operations and the railroad owned by McKell continued to grow during the early decades of the 1900's, Kilsyth became home to a sprawling mining and railroad repair shop complex located adjacent to the Kilsyth mine. Much of the old McKell repair shop complex remains standing today, including the former KGJ&E engine-house, one of a very few, and perhaps the only remaining engine-houses remaining in Southern West Virginia. Although Thurmond receives its notoriety for being the region's "historic railroad town," the community of Kilsyth actually contains a far greater number of historic railroad structures than does the present-day town of Thurmond. The huge twin-smokestacks, still standing in the center of the McKell complex at Kilsyth, grace the skyline serving as highly visible landmarks that can be easy spotted from miles away. The old smokestack are regarded by many as a eyesore, while others see them as one of the last remaining examples of the massive industrial edifices that was once was typical throughout the hillsides and valleys throughout Southern West Virginia.

The final chapter of saga of the McKell Coal & Coke Company was written in 1939, with the death of William McKell. Having never married, and having no children of his own, William McKell had not been able to groom a replacement for himself. Although the McKell coal empire had a vast amount of coal lands that had not yet been mined (most of it located in the Garden Ground area) the McKell coal empire ceased to function for lack of a new "king." The following year, the McKell heirs, having no interest in entering the coal business, sold the McKell Coal & Coke Company to the New River Company. Thus ended the reign of one of the area's pioneering coal companies that had a profound effect upon the towns of Mt. Hope and Kilsyth and virtually the entire region for more than four decades.