so before I answer this question, I need to make some important points here. I had this question since around September 2014, there are so many girl groups nowadays, but exactly how many? so I start to search some evidence on Internet and plus some of my own knowledge in the past. At the beginning I thought about Wikipedia since I believe they should have information of everything. But quickly I found out some girl groups I actually know back in late 90s to early 2000s are not listed in Wikipedia, but those girl groups did exist, I had cassette tape and CD of these groups as evidence before.
Then few weeks ago, I found out one very interesting article on Internet, this person starts a project since 2005, and which tracks all the kpop idol groups since 1980s until today, which is much better than Wikipedia. I was very curious about it, then I read through her article about old school kpop groups back in late 90s, I actually found out those groups I had cassette tape and CD before. Vast World of Kpop (I give full credits from that person here)
However in her article, it includes both boy groups and girl groups and mixed groups, and I don't really know boy groups as girl groups that much, so I extracted all the information about all girl groups from her article, and provide the evidence for my article.
Before I did serious research and count, I estimed I know probably around 100 girl groups.
Ok, so here we go:
1 The groups I marked as Red Bold are top tier girl groups which are really popular.
2 The groups I marked as Pink are girl groups I heard about it at some point , but don't know them quite well.
3 Normal font are girl groups do ever exist at some point in kpop history, but I never heard of.
4 I started since the first widely recognized girl group at 1996 and until 2014 last year.(since we are still at 2015 right now)
5 Any sub-unit/group will not be considered here. For Example: SNSD and TTS are considered as one group.
B.B(비비) was considered the 1st ever kpop girl group.(1996)
The 1st generation (debut from 1996 until 2001)
S.E.S at year 1997
1996: B.B, BOSS, ECO
1997: Baby Vox, Diva, Enue, Juliet, S.E.S, Sue, Tutti, Hans Band
1998: Circle, Cooki, Fin K.L
1999: AIDA, As One, Chakra, CLEO, F.O.X, Hush, See U, O-24, T.T.MA ,Tashannie
2000: HoneyBee, MINT, Papaya, Shamony, SZ, TINY
2001: AL, C.O.C ,D.U.B, Daisy, G.U.Y , Girl Fand, Jewelry, K.I.S.S, M.I.L.K, Nazka, S, Toya, VioxCo
For all the 1st generation kpop idol groups, I know 24 out of 43 groups, so 56%, which is not bad, especially almost all the kpop girl groups debut at year 1999, and that matches the time I am actually really into kpop.
The 2ed generation (debut from 2002 until 2006)
CSJH The Grace at year 20052002: BUDDY, Dejavu, FEVER, Isak N Jiyeon, J.S, LUV, ShinVi, Sugar, Swi.T
2003: Big Mama, Bubble Sisters, Lorelei, Morning, The Color, WID
2004: 7 Princess, ELF, Girls Friend, Heart, Shyne
2005: Almoner, Apple Jam, Casa& Nova, Dami & Junior, Gavy NJ, i-13, IRIS, KisFive, LADY, LPG, Orange, Perfume, Red Sox, S.Blush, CSJH The Grace, XR
2006: 2NB, ASIA, B.U.T, Baby B, BGH4, Brown Eyed Girls, CARA, Chapter 2, Foxy, ICE, J Lady's, Kirots, Maronie Girls, SeeYa
For all the second generation girl groups, I only know 16 out of 50 groups, which is only 16%, which is correct since I stop following kpop for a while since 2003 until SNSD came out, but I still know all the well known ones from this period. The only kpop CD I had from this period is Lee Hyori, but no groups.
The 3rd generation (debut from 2007 until 2011)
Girls' Generation aka SNSD at 20072007: Baby Vox RE.V , Black Pearl, CATS, Gavy Queens, Girls Generation, Illumina, KARA,Storm, TaeSaBiAe, Wonder Girls, Yes Girls
2008: Belle Epoque, Davichi, Eve&Sat, i-Coffee, Miss$ ,S5en, Swan,Wink
2009: 2NE1,4 Minute, 7Size, After School, Brand New Day, Cutie,Devil&Angel ,f(x), Flying Girls, HAM, Jewelry S, JQT, Lady Collection, Pink Heart, Rainbow, Secret, T-ara
2010: Aurora, B.Dolls, Bebe Mignon, BlackList, Chocolate, City Lady, Cutie-L, D.Heaven, EVAS, EZM, Fit Girls, Free Star, Girl Story, Girl's Day, Girl2School, GP Basic, HoneyDew , Miss A, Nine Muses, Queens, Sistar, Song Cry Girlz, Soul Lady, T-Angel, TEN, Troty, Twiny, VNT
2011: 2Boram, 5Dolls, APink, April Kiss, As Blue, As Red, BBAN, Bella, BGH To, Black Eye, Blady, Brave Girls, C-Real,Carcard Girl,Chi Chi, Chokolat, Coin Jackson, Dal Shabel, Ei Yo, Elizabeth, Eye To Eye, G.IAM, HaraSora, INY, Leaders, NEW P.O, Ocean Girls, Piggy Dolls, Rania, Stellar, Swincle, Swing Girls,Woman Power
I would say the 3rd generation girl groups are the most important girl groups, also the most popular ones nowadays are from this generation. Starts at year 2007,SNSD, KARA, Wonder Girls , the girl groups become a trend in kpop. Also, all my fav girl groups such as APink, Girl's Day are also from later in this generation. And I know 31 out of 98 groups, which is 32%, which is not bad. But some Groups I just never heard of here.
The 4th generation (debut from 2012 until now)
EXID at 2014
PameLA ,Pandora, PlayA , Puertty ,Ruby,S The One, SHE'Z , Six Bomb, Skarf, Spica, Sunny Days,
Superarls, TAHITI, The SeeYa, TINUS, Tiny-G, Two X, Valiant,Wow
2013: 2 Yoon,2EYES ,A-Dean,AGirls,ALTHEA, BESTie, BH BPPOP, DASONi, Delight, Duo Flow, F.W.S, Global Icon, Heart Rabbit Girls,Hidden Fantasy,K-Girls, Ladies' Code,Littles, Live High,LUSH, M&N , PASCOL,Peach Girls,Peernine, Pixie, Purplay, Queen BZ, Rainy,TINT, Tren-D, Turan,Veloce,WassUp
2014: 1PS, 4G,4L, 4TEN, A.KOR, AiRi, Alice White, BAD Kidz, BAY.B , Berry Good,Billion, BoB Girls,D.Holic, G-Friend, Girl Hood, Kiss&Cry, Laboum, Lip Service, Lodia, Lovelyz, LPG Chaness,Mamamoo, Melody Day, Minx,MOA, N*White, OuiGee, PRITZ, Purfles, Red Velvet, Step, Scarlet, Sonamoo , Strawberry MILH, SWITCH, Taurine,The Unnies, Vetty L, Wings,YE.A, Year Seven Class 1,
We are still at this generation right now, so even though I know a lot of girl groups from this period. But way too many girl groups right now, just way too many. only from 2012 to 2014 these 3 years alone, there are 129 new girl groups debut in 3 years, and 70% I don't even know. I know 31 out of 129 new debut girl groups.which is only 24% , but I think it's already pretty good.
so Let's do the simple math. all the kpop girl groups I know since 1996 until now are 24 + 16 + 31 + 31 = 102, so I am correct. And all the girl groups ever exist are 43 + 50 + 98 + 129 = 320, which means there are at least 320 kpop girl groups ever exist from 1996 until 2014.
Note: Based on this, I know there will be around over 800 boy groups ever exist, since there are way more boy groups than girl groups, especially back in old times, I believe there are only slightly less than 3 times the number of girl groups . (I can't count this since there are just way too many and I'm not really into boy groups ) And plus mixed groups, the total number should be somewhere between 1250 to 1300....
You could use my information to count how many girl groups do you know ? If you know over 50 out of 320 , it's pretty much a lot already.