Its headwaters are three separate forks that begin in Kentucky and converge in Baxter, KY, located in Harlan County. Martin's Fork starts near Hensley Settlement on Brush Mountain in Bell County and snakes its way north through the mountains to Baxter. Clover Fork starts on Black Mountain in Holmes Mill, near the Virginia border, and flows west in parallel with Kentucky Route 38 until it reaches Harlan. Clover Fork once flowed through downtown Harlan and merged with Martins Fork at the intersection of Kentucky Route 38 and US Route 421 until a flood control project began in 1992 diverted it through a tunnel under Little Black Mountain from which it emerges in Baxter and converges with Martins Fork. Poor Fork begins as a small stream on Pine Mountain in Letcher County near Flat Gap, Virginia. It flows southwest in parallel with Pine Mountain until it merges with the other two forks in Baxter.
Confluence of the Cumberland River at Baxter
From there, the wider, now named Cumberland River continues flowing west through the mountains of Kentucky before turning northward toward Cumberland Falls. The 68-foot (21 m) falls is one of the largest waterfalls in the southeastern United States and is one of the few places in the Western Hemisphere where a moonbow can be seen.
Beyond Cumberland Falls, the river turns abruptly west once again and continues to grow as it converges with other creeks and streams. It receives the Laurel and Rockcastle rivers from the northeast and then the Big South Fork of the Cumberland River from the south. From here it flows into the man-made Lake Cumberland, formed by Wolf Creek Dam. The more than 100-mile (160 km) reservoir is one of the largest artificial lakes in the eastern US.
Near Celina, the river crosses south into Tennessee, where it is joined by the Obey River and Caney Fork. Northeast of Nashville, the river is dammed twice more, forming Cordell Hull Lake and Old Hickory Lake. After flowing through Nashville and picking up the Stones River, the river is dammed to form
Cheatham Lake. The river turns northwest toward Clarksville, where it is joined by the Red River, and then flows back into Kentucky at the Land Between the Lakes National Recreation Area, a section of land nestled between Lake Barkley, which is fed by the Cumberland River, and Kentucky Lake. Finally, the river flows north and merges with the Ohio River at Smithland, northeast of Paducah.