April 1, 1959:  Plans unvieled by the Missouri State Highway Commission called for a 40-mile loop around St. Louis.  The plans called for a new bridge over the Mississippi River at Chain of Rocks.

1960-62:  Construction takes place throughout North County

October 3, 1962:  The section of 270 from I-70 to Bellefontaine opens to traffic.

October 1964:  The section of 270 from Route 3 to I-55 opens.

Late 1964-Late 1969: I-244 slowly opens in segments.

September 2, 1966:  The new Chain of Rocks Bridge opens, completing I-270.

1967:  I-255 opens from I-55 to Telegraph Road.  The segment from Telegraph to Koch opens a few months later.

1969:  I-244 is completed.

1974:  the nationwide renumbering schemes hit St. Louis.  The entire beltway system is absorbed as 270.

1980:  The interchange with 70 and 270 is rebuilt.

1982:  Apparently, IDOT decides to make their own plans.  They consider renumbering a portion of 270 near Glen Carbon to I-870, but the locals apparently told them to forget it.  Eventually, IDOT settled on numbering the eastern bypass as 255.

September 1984:  The westbound span of JB Bridge opens to traffic.  The section of 255 from Columbia to I-64 opens shortly after this event.

November 1986:  A section of 255 from 64 to 55/70 opens to traffic.

1988-1993:  The 270-Highway 40 interchange is rebuilt.

March 1988:  The section of 255 from 55/70 to Horseshoe Lake Road is open to local traffic only, in an effort to permit locals to avoid the bridge replacement project on 157 just north of Beltline Road in Collinsville.

July 26, 1988:  The section of 255 from 55/70 to 270 is opened to traffic with tons of fanfare.  The "antique car parade" ties up traffic on westbound 270 between 111 and 157 for several hours that afternoon.  The section of 270 from 111 to just east of 157 is widened from 4 lanes to 6 lanes -- the only section in Illinois that got any major change.

1992-1994:  The 55/270 interchange is rebuilt, along with the 55/Lindbergh interchange.

Summer 1993:  The Great Flood of 1993 ravaged that spring and summer in the Mississippi River valley.  Despite the lower than normal crossing over the Mississippi River, the 270 bridge over the river is the only bridge from Granite City to Burlington, IA that remains open throughout the flood.  Choateau Island is submerged throughout the majority of the flood, which attracts gawkers.

1998-2001:  The 270/44 interchange is rebuilt.

September 13, 1999:  The event that probably sped up reconstruction efforts of the 270-170 interchange happened when a massive chain-reaction accident on the westbound lanes in front of St. Thomas Aquinas Mercy High School leaves three people dead and six injured, and paralyzed traffic in North County for several hours.

February 2002-Late 2003:  The 270-170 interchange is totally reconstructed, resulting in closures in three of the four ramps of the interchange at one point or another.