If you are, fortunately for everyone, alive today, and you write and publish poetry, you are a 21st century poet. Other poets, less lucky, have died in the last 100 years or so, but their great contribution to poetry continues. Poems, of all the literary art forms, are perhaps the most generous gifts, because compared to the energy and effort involved in their creation, the material returns are the least - so they stand as bequests to eternity, or at least, posterity.
Even a weak, or minor, poet may create a poem or three that are wonderful, moving, crafty, cunning, potent, convincing, wise, helpful, funny or delightful - but below is a list of 175 poets, who have written in the English language primarily, who published most of their poetry in the 20th century, and are no longer with us, who gave us whole collections that were and are vital and necessary to read.
No doubt another 25 or more poets from Canada, America, Ireland, Great Britain, New Zealand, Australia, South Africa, and beyond, could flesh out a viable "canon" of 200+ 20th century English-language poets we should all read, but I think this list forms a very good start, and includes poets of all schools, styles, decades, eras, genders, and political leanings, more or less.
While debates will hopefully always continue in academic and critical circles about the value of certain poets and poems in terms of adding to the general literature of their age (where is Newbolt?), it seems, looking at this list, unlikely any new very major poets from the period under observation will appear, though a few very good lesser poets may receive their due. Terence Tiller, for example, is a seriously good, very brilliant and exciting poet, and when I publish his Collected Poems next year, his canonical status should be re-established. But he is not ever going to (it seems likely) be read as more significant than, say, near-contemporaries like Auden, Douglas or Larkin - partially because his impact on his time, his contemporaries, was less. His influence if it arrives, will be more posthumous, as was Hopkins.
Please let me know who you would want to see added. This is of course not a definitive list. But none of these 175 can really be left out. Happy Easter!
175 KEY ENGLISH-LANGUAGE POETS OF THE 20TH CENTURY (DECEASED)
EDGAR LEE MASTERS
EDNA ST VINCENT MILLAY
EDWIN ARLINGTON ROBINSON
GEORGE MACKAY BROWN
IAN HAMILTON FINLAY
JAMES K BAXTER
JOHN CROWE RANSOM
LEROI JONES/AMIRI BARAKA
MELVIN B TOLSON
ROBERT PENN WARREN
WALTER DE LA MARE
WILLIAM CARLOS WILLIAMS