The building, at the corner of West Main and Broadway streets, reverted to the county after CDF moved to its new location in the Fairpark District.
County supervisors voted earlier this year to move their offices, as well as the county administrator's office, to the facility after renovation.
They're currently housed at the Lee County Justice Center.
Pryor & Morrow Architects of Tupelo presented a cost estimate of the work, which involves an upgrade to the building's ceilings, doors, floors, walls, plumbing, electrical and lighting system and bathrooms.
It also involves some light demolition but otherwise leaves the interior structure unchanged.
Costs will rise, however, if it's determined the building needs a new roof or a new heating-and-air system, said architect Charlie Watson.
Supervisors unanimously approved the work plan and cost estimate during their meeting Monday at the Lee County Justice Center.
Pryor amp& Morrow is expected to return to the board in June with construction bids, and work could begin as early as July.
The project is slated to take 90 days.
Supervisors could move into their new space by October or November.