The Starfleet Ground Forces is the branch of Starfleet concerned with ground based combat.
The Ground Forces uses a similar departmental structure as Starfleet, with Command, Operations and Sciences. It also has more specialized units apart from the ordinary infantry. It has air, artillery and mechanized units to support the soldier on the ground. It also has electronic warfare units, whose role is to intercept and jam enemy transmissions (including transporters) and to make sure the Ground Forces' own signals can reach their destination. (LUG RPG: The Dominion War Sourcebook: The Fires of Armageddon)
The Ground Forces are organised in units of various sizes, from the smallest to the largest they are:
At the start of the Dominion War the Ground Forces numbered 200,000 personnel, which was rapidly increased to 250,000 after the scope of the war became more apparent. By the end of the war the Ground Forces had lost over 105,000 soldiers but due to decent recruitment through the conflict it still had 174,300 combat personnel in service. (The Dominion War Sourcebook: The Fires of Armageddon)
During the Federation-Klingon War in the 2400s, Lieutenant Commander Kanril Eleya suggested to Admiral Stephen Alcott that the Ground Forces be used in an "end run" around the Colonist Act of 2371 as a way to stiffen the defenses of planets bordering the Klingon Empire. This plan involved recruiting and training local colonists as Ground Forces reservists who could be called up in the event of attack. The idea came to her after the Battle of Gamma Hromi IV earlier in the war, and she proposed it to Alcott in October 2406 after interrupting a Klingon-Orion raid on Rabaul III that destroyed the colony of Turtle Bay. (The War of the Masters: "Sound the Alarm")
The Ground Forces rank structure differs from that of Starfleet. The officer ranks in ascending order are: ensign, lieutenant JG, lieutenant, captain, major, colonel, general. The officer that commands the entire Ground forces is given the rank Commanding General. (The Dominion War Sourcebook: The Fires of Armageddon)