Formed in the 1950s, the first section was opened in the early 1960s on the Missouri side of the river. In 1964, sections on the Illinois side of the river were completed. Construction on the section from I-70 near Maryland Heights to I-55 in Troy was finished by 1968, which completed the original section of I-270. The north/south section at this time was Interstate 244, which was completed in November 1968<ref>Southeast Missourian Archives</ref>.
Between 1974 and 1976, the local transportation officials decided to drop the 244 and 255 designations and the entire beltway was 270. Federal Highway Logs soon reflected it<ref>Route Log and Finder List, Interstate Highways, USDOT, 1978<ref>. However, during this time, planners up in the River Bend started making their own transportation plans, which included building the Berm Highway, McAdams Parkway Extension, and the Alton Bypass. Although the final one was more of a pipe dream due to funding at the time, the plans would eventually affect the numbering of what eventually became the 270-255 Loop.
Since then, changes in driver habits led MoDOT to widen the highway west of Lilac during the 1980s and 1990s. On the Illinois side of the river, little has changed except for the section from IL 111 to IL 157 which was widened in 1987-1988. There are talks, however, of widening 270 between Lilac and IL 111, which is the only section of the 270-255 Loop that is still at 4 lanes of traffic.
Like Highway 40, 270 has seen its fair share of not so memorable events. These events listed below stand out above the rest:
- 10 August through 14 August 1994. A broken beam on the Chain of Rocks Bridge shut down all but 1 lane of the bridge for four days, forcing traffic to clog alternate routes. This incident happened late Wendesday night, and the news the following morning gave drivers from the Metro East the rude surprise they did not want. Even after the lanes reopened from the emergency repairs, the woes continued for the remainder of the month and IDOT ended up doing major work on 270 from 255 to Lilac from 1996 through 1998.
- 13 September 1999. A massive chain-reaction crash occurred at the former St. Thomas-Aquanias Mercy High School in the middle of morning rush hour, resulting in multiple fatalities and paralyzed traffic for several hours. This incident sped up the reconstruction of the 270-170 interchange between 2001-2004.
- 28 October 2002. A FedEx truck caught fire east of 367, causing panic that resulted in major delays.
- 4 February 2008. Foggy weather caused several wrecks on a section between I-55/70 and IL 159, closing the highway for 2 hours.
- 8 December 2010. A tractor-trailer accident involving a fatality shuts down the Chain of Rocks Bridge right before the morning rush hour. It remained closed until the afternoon rush hour started. The traffic was forced to the other bridges for 10 hours and it resulted in 9 mile long backups on sections of IL 143 and I-55/70.