The city center is approximately two miles east of the intersection of Interstate 64 and U.S. Route 50. Suburban growth in O'Fallon expanded considerably during the 1980s and following the expansion of Interstate 64 in the 1990s. Subdivisions include Thornbury Hill, Nolin Creek Estates, Fairwood Hills, Deer Creek, Forest Hills, and Fairwood East. O'Fallon Township High School's main campus at 600 South Smiley Street has undergone numerous additions over the past decades to ease overcrowding, including the creation of the separate 9th Grade Milburn Campus.