[59] Carlin entered the series with two full-time Chevrolet-powered entries for the 2018 season, running ex-Chip Ganassi Racing drivers Max Chilton and Charlie Kimball.

[61] Following the Road America round, Barnhart confirmed rumours that they wish to expand to fielding two cars as early as the latter part of the 2018 season, specifically naming Sonoma.

[63][64] On January 5, 2018, Juncos announced Formula V8 3.5 driver René Binder would contest the races in St. Petersburg, Barber, Mid-Ohio, and Toronto, with an entry at Detroit being confirmed later.

[18] After competing in road and street courses only for Ed Carpenter Racing in 2017, Spencer Pigot made his full-season début with the team, replacing J. R. Hildebrand in the No.

[14] After six seasons in the German Deutsche Tourenwagen Masters, Robert Wickens made the switch to IndyCar to drive the No.

Wickens suffered severe injuries in a crash at the 2018 ABC Supply 500 and was forced to miss the rest of the season.

On August 29, SPM announced Carlos Muñoz as Wickens' replacement in the #6 car at the Portland and Sonoma rounds.

[49] On November 16, 2017, A. J. Foyt Enterprises announced that Brazilian Indy Lights driver Matheus Leist would drive the No.

After six seasons with Stewart-Haas Racing in NASCAR, Danica Patrick announced intentions to return to the Indianapolis 500 for the first time since 2011.

[67] After spending one season with A. J. Foyt Enterprises, Carlos Muñoz rejoined Andretti Autosport for the Indianapolis 500.

The #19 was driven by Zachary Claman DeMelo, who partook in the 2017 Indy Lights season with Carlin and the 2017 GoPro Grand Prix of Sonoma with Rahal Letterman Lanigan Racing, in the other 10 events.

On March 20, 2018, it was announced Pippa Mann would drive a 4th car for Dale Coyne Racing at the Indianapolis 500, with sponsorship from Donate Life Indiana.

[15] On May 10, Juncos Racing announced that Alfonso Celis Jr. would make his IndyCar debut with the team at Road America.

[69] On July 10, Harding Racing announced that Conor Daly would replace Gabby Chaves for round 12 in Toronto.

They want to test current top three Indy Lights drivers Colton Herta, Santiago Urrutia and Patricio O'Ward, the latter having already received a seat fitting with the team.