Lexington County Administrator Joe Mergo will step down at the end of the year.

In a letter to the staff, Mergo said he had “an exciting opportunity in the private sector.”

Mergo will start as chief operating officer at Nephron Pharmaceuticals in Lexington County Jan. 4.

He leaves a public sector job earning $210,000 a year.

His Nephron compensation has not been disclosed.

Mergo had served 5 years as deputy administrator and became administrator in March 2012.

The County Council decided to stay with Mergo as its top aide instead of looking elsewhere.

Mergo became administrator 2 months after taking over supervision of county employees in what was billed as a tryout.

He previously held other supervisory posts in trash collection and animal control.

A pending decision may continue a trend of county council selecting their top aide from within instead of going outside.

The council has not said what it intends to do this time.