Gianlupo,
I'm not a native of Monticello, Arkansas. The family and I moved here about 12 years ago. I always assumed that it derived its' name from Thomas Jefferson's Monticello, but one should never assume.
This is a fairly old community, by American standards, and predates the Civil War by several decades. I have found tombstones in a local cemetery that have dates from the time of Andrew Jackson's presidency.
Regards, Shuckins