It's not even on the map, but Cool Springs is one of the fastest growing and most affluent cities in the country. OK. technically, it's not a city. Cool Springs saddles the border of Franklin and Brentwood in Williamson County, TN, which, depending on who you ask, is either the 9th, 11th or 17th wealthiest county in the nation. No matter who's right, there's definitely a little disposable income around here and every kind of store, restaurant, business service known to mankind is rushing in. Just a few years ago, the entire area was nothing but cow fields, but in 1991, The CoolSprings Galleria Mall opened and the race was on. Cool Springs now has car dealerships, luxury hotels, office buildings, apartments, condos, luxury homes and strip malls as far as the eye can see. In 2008, Cool Springs became home to Nissan's North American Headquarters.