Thee and Thou are still used in Northern England (Yorkshire and Lancashire). Although probably only by older people and often spoken as Thi and Tha.
Interesting, and are those used as the informal you? Or in reference to singular?
Old Yorkshire phrase for telling children to mind who they address as 'thee / tha': "Don't thee tha them as thas thee" - kind of a similar sense as 'mind your Ps and Qs'.