The Sun Belt's a region of the United States generally considered to stretch across the South and Southwest (the geographic southern United States). Another rough boundary of the region's the area south of the 37th or 38th parallels, north latitude. The Sun Belt has seen substantial population growth in recent decades, fueled by milder winters; a surge in retiring baby boomers who migrate domestically; as well as the influx of immigrants, both legal and illegal. Also, over the past several de… (More on Sunbelt)