Chart of Utah major cities and towns population (2010)

The three fastest-growing counties from 2000 to 2010 were Wasatch County (54.7%), Washington County (52.9%), and Tooele County (42.9%). However, Utah County added the most people (148,028). Between 2000 and 2010, Saratoga Springs (1,673%), Herriman (1,330%), Eagle Mountain (893%), Cedar Hills (217%), South Willard (168%), Nibley (166%), Syracuse (159%), West Haven (158%), Lehi (149%), Washington (129%), and Stansbury Park (116%) all at least doubled in population. West Jordan (35,376), Lehi (28,379), St. George (23,234), South Jordan (20,981), West Valley City (20,584), and Herriman (20,262) all added at least 20,000 people.

Reference 1: Population (2010) within city limits, Population density (/mi2) and Population density (/km2).

Reference 2: Salt Lake City, West Valley City, Provo, West Jordan, Orem, Sandy, Ogden, St. George, Layton and Taylorsville.

Source: http://en.wikipedia.org/wiki/Utah