The 2011 In-House Counsel Barometer, by Davies Ward Phillips & Vineberg in association with the Canadian Corporate Counsel Association, includes responses from 864 lawyers in Canada. Of them, 295 were with publicly traded companies and 206 private. Public companies likely having larger law departments, this survey, which looked at individual responses not at responses by law department, may have had more multiple respondents from public than from private companies. Perhaps the ratio is about one to one.
If so and if something like that ratio might hold true in the United States, I believe there are a bit more than 4,000 U.S. companies listed on its various stock exchanges (although as I write this I can’t explain the Wilshire 5000). Perhaps, then, with one privately held company with a law department for each publicly traded company, we could estimate 8,000 corporate legal departments? The logic and fact basis are both tenuous, but somewhere there may be data on the ratio and we can narrow the range of uncertainty.