A form system is provided for forming a structural column assembly of the type used for erecting building structures and the like, such as a concrete column or footing formed in situ in an earthen hole. The system includes a support system, including a wire support member and an associated base foam ring having an offset center hole corresponding to the centerline of the concrete footing, which is placed at the bottom of the earthen hole. A lower vertical form system, including multiple interlocking pieces, is assembled and joined at one end to an offset disk member. The disk member of the lower vertical form system is then placed onto the base foam ring in abutting engagement. The form system is then plumbed and positioned, e.g., in relation to one or more layout strings. Once the form system is in the correct position, the earthen hole is backfilled, e.g., with dirt or other material, thus holding the properly positioned form system in place. The lower vertical form system is then cut to grade. Reinforcing assemblies, such as rebar, can then be inserted into the lower vertical form system. Concrete can then be poured into the lower vertical form system, thus forming a lower portion of the concrete column or footing. An upper vertical form system can then be used to form the upper portion of the concrete column or footing, e.g., that portion that is above grade.