You have a couple of problems with this I think. AL worksheet appears to have Cities in column B and counties in column A but the other two seem to be the other way round (although headers are the same).

You need these to be consistent and for VLOOKUP to work you need cities in one column (e.g. A) and counties in a column to the right (e.g. B).

You also appear to have a space in the AL worksheet name, i.e. AL[space], this complicates things further.....

sort out these problems and you should be able to use a formula like this in custmast K2 copied down the column

=VLOOKUP(E2,INDIRECT(F2&"!A2:B1000"),2,0)

As it stands you need to use this

=INDEX(INDIRECT("'"&F2&" '!a2:a1000"),MATCH(E2,INDIRECT("'"&F2&" '!b2:b1000"),0))

....and it still won't work on all entries