1850 Federal Census Enumeration District descriptions. Where can I find them?

In attempting to narrow the locations of multiple families of interest it would be helpful to know the geographical boundaries of the enumeration districts within a county.  Specifically I'm looking for these descriptions for districts in Monroe County, Virginia for 1850.  I understand that maps were not crated until the very earliest in 1880, but the districts did have "descriptions".  This is what I'm looking for.