R.L. Polk & Co. is a privately held company founded in Detroit, Michigan (currently based in Southfield, Michigan) that collects and interprets automotive data and provides them, along with marketing services, to automotive and related industries worldwide. Over its history, Polk has also published city directories, state gazetteers, and directories to other businesses and industries, in addition to involving itself in direct marketing efforts (in 2000, Polk sold its non-automotive statistics divisions to Equifax).
From the description of R.L. Polk & Co. vehicle registrations collection, 1926-1967 (bulk 1930-1967) (The Henry Ford). WorldCat record id: 76876664