The most common and most likely answer to this crossword clue is the 6 plus 4 letter word COUNTY SEAT
I've seen this crossword clue in Independent
C
O
U
N
T
Y
S
E
A
T
Buddy explains!
The straight part
We know that "Important US town" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case important us town = county seat.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.