|Stage Name||Birth Name||Position||Birthday||Age||Height||Star Sign Sort descending||C Y||BT|
|Viva 비바||Hwang Jiwon||Dancer||18||166 cm or 5'5½"||Aquarius||Dragon||A|
|Jiwon 지원||Kim Jiwon||Visual||19||164 cm or 5'4½"||Aries||Hare||O|
|Nayoon 나윤||Hwang Nayoon||Vocal, Dancer||19||Aries||Hare||O|
|Chaesol 채솔||Moon Chaesol||Sub-vocal||19||169 cm or 5'6½"||Cancer||Tiger||A|
|Cherry 체리||Kim Chaeyoung||Dancer||20||Cancer||Ox||B|
|Genie 지니||Kim Jiwon||Visual||21||168 cm or 5'6"||Capricorn||Rat||B|
|Heejin 희진||Song Heejin||Leader, Vocal||22||162 cm or 5'4"||Leo||Pig||B|
|Bomin 보민||Kim Bomin||Sub-vocal||16||Libra||Snake||AB|
|Haeun 하은||Kim Haeun||Vocal||18||Libra||Hare||B|
|Lucky 럭키||Jin Hyunjoo||Dancer, Maknae||16||161 cm or 5'3½"||Scorpio||Snake||A|
Good Day 굿데이 is a ten-member female idol group formed by C9 Entertainment. They debuted on August 30, 2017, with their 1st mini album All Day Good Day.
In 2012, Haeun was part Nega Network's 3-member girl group Littles, which never debuted. The group's only release was an OST for the drama "The Great Seer."
In 2013, Heejin took third place on "Superstar K5." Bomin acted in No Breathing in the role of a younger version of Yuri's character.
In 2015, Heejin released her debut single, "To Reach You," featuring the rapper Olltii. She also sang OSTs for the dramas "Late Night Restaurant" and "Into the Flames."
Jiwon has been a model for the teenage fashion online shopping portal Sonyunara since before debut.
In July 2017, C9 Entertainment announced the launch of their first female idol group, C9 Girls. On July 7, members Genie and Nayoon were revealed, alongside the group name: Good Day. On July 10, members Bomin, Jiwon, and Lucky were revealed. On July 11, members Cherry, Chaesol, and Viva were revealed. On July 12, members Heejin and Haeun were revealed. On July 15 and 16, the group revealed the members' clean version teaser photos and B-cut teaser photos respectively. From July 20 to August 10, on Thursdays, 4 episodes of their reality show, "Good Day 2 U," was shown on C9 Entertainment's V App channel.
On August 30, they debuted with their 1st mini-album, All Day Good Day, with the music video for their debut track "Rolly" featuring the appearance of C9 Entertainment trainee and current Wanna One member Bae Jinyoung. The other 3 tracks from the mini-album are songs from the group's 3 units: Good Morning, Good Night, and Midnight. On September 3, they held their debut mini-concert All Day Good Day at the Yes24 Live Hall.
Six members (Heejin, Genie, Chaesol, Jiwon, Viva, Lucky) joined the reality television series "The Unit." All except Lucky passed the Boot Evaluations in episode 1.[However, Lucky was revived from her elimination.
On November 1, it was announced that Nayoon will take a break from the group's activities due to a tear in her ligament during practice.