Methods and apparatus are disclosed for distributing entries among lookup units and selectively enabling less than all of the lookup units when performing a lookup operation. Each of the lookup units is assigned a subset of the possible values of the entries and is programmed with the corresponding entries. In performing a lookup operation on a lookup word, only the lookup units possibly containing a matching entry are enabled which saves power and dissipates less heat. A lookup operation is then performed in the enabled lookup units to generate the lookup result. A lookup unit may correspond to an associative memory device, an associative memory bank, sets of entries within one or more associative memory devices or banks, a lookup control and a memory device, and/or any other lookup mechanism. In one implementation, the partitioning of elements is based on a Patricia tree representation of the possible entries.