Al Unser, Sr. dominated the race, winning the pole position and leading 190 laps en route to victory. He joined his brother Bobby as the first duo of brothers to win the Indianapolis 500. It was the first of four victories for Al at Indianapolis. Car owner Parnelli Jones, who won the race as a driver in 1963, became the second individual (after Pete DePaolo) to win separately as both a driver and as an owner.

Unser took home $271,697 out of a record $1,000,002 purse. For the first time in Indy history, the total prize fund topped $1 million.

Rain on race morning delayed the start by about thirty minutes. On the pace lap, Jim Malloy smacked the outside wall in turn four, which delayed the start further.

All 33 cars in the field were turbocharged for the first time. This would be the final 500 in which the winner celebrated in the old victory lane at the south end of the pits. Victory lane would be relocated for 1971.

The race start time was scheduled for 12:00 noon local time, a slight departure from the traditional 11:00 am start time that was used during most of the 1960s. With the race scheduled for Saturday May 30, Speedway management announced that Sunday May 31 would be the designated rain date, the first time the race would be permitted to run on a Sunday. However, despite a brief rain delay on race morning, the full 500 miles was completed Saturday, and Sunday was not needed.

This would be the last Indy 500 that was scheduled for the traditional fixed date of May 30. Through 1970, Memorial Day was a fixed date holiday observed on May 30 regardless of the day of the week. For 1970, the date of May 30 fell on a Saturday. From 1911 to 1970, the race was scheduled for May 30, regardless of the day of the week, unless May 30 fell on a Sunday. In those cases, the race would be scheduled for Monday May 31. The Uniform Monday Holiday Act would take effect in 1971, and for 1971 and 1972, the race would be scheduled for the Saturday of Memorial Day weekend. In 1973 it was scheduled for Monday (but rain delayed it until Wednesday). From 1974 onward, it was scheduled for the Sunday of Memorial Day weekend. From 1974 onward, the race would only be held on May 30 if that date fell on a Sunday.

...
Wikipedia