A Corps Support Group, or CSG, was a brigade

Brigade

A brigade is a major tactical military formation that is typically composed of two to five battalions, plus supporting elements depending on the era and nationality of a given army and could be perceived as an enlarged/reinforced regiment...

-sized unit in the United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

. A CSG differs from a DISCOM in that it is a corps

Corps

A corps is either a large formation, or an administrative grouping of troops within an armed force with a common function such as Artillery or Signals representing an arm of service...

, not a divisional

Division (military)

A division is a large military unit or formation usually consisting of between 10,000 and 20,000 soldiers. In most armies, a division is composed of several regiments or brigades, and in turn several divisions typically make up a corps...

, asset. Doctrinally, a CSG serves corps units, not division units, but in practice CSGs typically have a close working relationship with a particular division especially in garrison. A CSG's subordinate units also may be parceled out to different commands in theater, thus their wartime organization will normally significantly differ from their garrison organization.

Typically, a CSG and its subordinate units will only deploy as far forward as the Division Support Area.
A typical CSG will be organized with a Headquarters Company and a varying number of Corps Support Battalions (CSB's) which may or may not be from the same Fort as the headquarters.
The CSG is normally responsible for reinforcing the logistics units of a Division while primarily supporting the non-divisional units such as Corps Artillery, Corps Military Police, and other higher echelon units.

The US Army has been transforming

Transformation of the United States Army

Army Transformation describes the future-concept of the United States Army's plan of modernization. Transformation is a generalized term for the integration of new concepts, organizations, and technology within the armed forces of the United States....

 many CSG's into Sustainment Brigade

Sustainment Brigade

As part of the early 21st century transformation of the United States Army from a division-based structure to a brigade-based army; the Division Support Commands, Corps Support Groups, and Area Support Groups are being inactivated or transformed to Sustainment Brigades As part of the early 21st...

s while Corps Support Battalions are becoming Combat Sustainment Support Battalions (CSSBs).