A commonplace holds that half the lawyers practicing law privately in the United States, meaning not as an employee of a company, government agency or other entity, practice solo. Behind the shingle is a single. It may be that half the internal law departments – using an expansive term “department” – are also lawyers practicing solo.
One-lawyer departments make sense if there is a power-law distribution of law departments by size (See my post of April 27, 2010: power-law distributions with 6 references.). One lawyer departments make sense if that solitary lawyer wears multiple hats. One lawyer departments, finally, are necessary stages for all larger departments to have passed through; you have to hire the first one to get to two lawyers, three, and more.