One of the hidden gems of the Silver Age.
While Supergirl did have her own serial in the pages of Action Comics, this isn’t a complete chronological retrospective.
Reviews were not always published in order and I’m not reviewing every single appearance.
The list below includes all reviews in order of publication, not in order of review, so expect spoilers for fifty year old stories.
Superman 123 (prototype)
Action Comics 252 (first appearance: reviewed last, so spoilers!)
Action Comics 253 (second appearance)
Action Comics 256 (first Dick Malverne)
Action Comics 258 (Supergirl exiled for talking with Krypto)
Action Comics 260
Action Comics 262 (origin of Superman’s powers revealed)
Action Comics 264
Action Comics 267 (part of the Legion retrospective)
Action Comics 269 (first Jerro)
Action Comics 272
Action Comics 273
Action Comics 276 (part of the Legion retrospective)
Action Comics 279 (Supergirl is adopted)
Action Comics 280
Action Comics 281
Action Comics 282
Action Comics 285 (existence revealed to the world)
Action Comics 287 (part of the Legion retrospective)
Action Comics 289 (part of the Legion retrospective)
Action Comics 295 (Lena Luthor)
Action Comics 296
Action Comics 297
Action Comics 298
Action Comics 299
Action Comics 301 (Super-Horse turned human)
Action Comics 309 (Supergirl’s biological parents return)
Action Comics 310
Action Comics 311 (Super-Horse turned human, AGAIN)
Action Comics 317
Action Comics 318 (Supergirl goes to college)
Action Comics 335
Action Comics 336
Action Comics 340
Action Comics 357
Action Comics 361
Action Comics 375
Action Comics 376
Adventure Comics 387-388
Adventure Comics and Supergirl’s costumes
Supergirl v1 #1-9
Supergirl v1 #10
Superman Family 165
Superman Family 168
Superman Family 171
Superman Family 177
Superman Family 206 (last Lesla-Lar)
Superman Family 207 (part of the Legion retrospective)
Superman Family 208
Superman Family 211-212
Superman Family 213-214 (last Lena Luthor)
Superman Family 222
Supergirl v2 #1-3
Supergirl v2 #10-12 (Tiny Clones)
Supergirl v2 #13
Supergirl v2 #14-15 (Blackstarr)
Supergirl v2 #22-23
DC Comics Presents #28 (Warworld)
DC Comics Presents #86 (last Supergirl story set before Crisis)
Crisis on Infinite Earths #4/5/6
Crisis on Infinite Earths #7 (death)
Superman #415
Bonus:
Pink Kryptonite
World’s Finest #169 (first team-up with Batgirl)
World’s Finest #176 (team-up with Batman…kinda)
Superman v2 #21-22 (debut of the post-Crisis “Matrix” Supergirl)