On Tuesday, privately held Seattle company Cobalt completed its $400 million cash sale to Automatic Data Processing, a publicly traded company based in Roseland, N.J.

On Tuesday, privately held Seattle company Cobalt completed its $400 million cash sale to Automatic Data Processing, a publicly traded company based in Roseland, N.J.

Cobalt, a 15-year-old digital marketing company focused on the automotive sector, employs about 1,000 people — 758 in Washington state.

The company will be moving its headquarters from Seattle’s SoDo neighborhood to a building at 605 Union Square in Seattle’s International District and plans to occupy it at the start of 2011, said John Holt, Cobalt’s CEO and now leader of ADP’s digital marketing group. The new space will consolidate office space it has in SoDo and Lynnwood. It also has 42 positions open, primarily in software development, digital advertising and business data analysts.