Looking at another post I was able to get what I wanted with the following code...
Select Distinct Top 1000000 tblADusers.Username,
  tblADusers.Userdomain,
  Max(tblCPlogoninfo.logontime) As 'last logon'
From tblADusers
  Inner Join tblADMembership On tblADMembership.ChildAdObjectID =
    tblADusers.ADObjectID
  Inner Join tblADGroups On tblADMembership.ParentAdObjectID =
    tblADGroups.ADObjectID
  Inner Join tblCPlogoninfo On tblCPlogoninfo.Username = tblADusers.Username And
    tblCPlogoninfo.Domain = tblADusers.Userdomain
Group By tblADusers.Username,
  tblADusers.Userdomain