Hello *benj,

You had the part that writes the file name to the worksheet in an IF statement checking it against the variable Acct. Since Acct was not set to anything, nothing ever matched. I corrected the code.
Sub ListFileNames()

  Dim FileName As String
  Dim FilePath As String
  Dim Valid As Boolean
  Dim Wks As Worksheet
  
    R = 1    'Starting Row
    Set Wks = Worksheets("Sheet1")
    FilePath = "C:\test" & "*.txt"
       
     FileName = Dir(FilePath)
     
     Do While FileName <> ""
       Valid = FileName Like "*_######.txt"
         If Valid Then
            Wks.Cells(R, "A") = FileName
            R = R + 1
            Acct = Mid(FileName, 6, 6)
         End If
       FileName = Dir
     Loop
     
End Sub