These are num­bers of Friends in Cana­da and the Unit­ed States (includ­ing Alas­ka, which was tal­lied sep­a­rate­ly pri­or to state­hood) com­piled from Friends World Com­mit­tee for Con­sul­ta­tion. I dug up these num­bers from three sources:

• 1937, 1957, 1967, 1977, 1987 from Quak­ers World Wide: A His­to­ry of FWCC by Her­bert Hadley in 1991 (many thanks to FWC­C’s Robin Mohr for a scan of the rel­e­vant chart).
• 1972, 1992 from Earl­ham School of Reli­gion’s The Present State of Quak­erism, 1995, archived here.
• 2002 on from FWCC direct­ly. Note: Cur­rent 2017 map.

Friends in the U.S. and Canada:

• 1937: 114,924
• 1957: 122,663
• 1967: 122,780
• 1972: 121,380
• 1977: 119,160
• 1987: 109,732
• 1992: 101,255
• 2002: 92,786
• 2012: 77,660
• 2017: 81,392

Friends in Amer­i­c­as (North, Mid­dle South):

• 1937: 122,166
• 1957: 131,000
• 1967: 129,200
• 1977: 132,300
• 1987: 139,200
• 2017: 140,065

You could write a book about what these num­bers do and don’t mean. The most glar­ing omis­sion is that they don’t show the geo­graph­ic or the­o­log­i­cal shifts that took place over time. Mid­west­ern Friends have tak­en a dis­pro­por­tion­ate hit, for exam­ple, and many Philadelphia-area meet­ings are much small­er than they were a cen­tu­ry ago, while inde­pen­dent meet­ings in the West and/or adja­cent to col­leges grew like wild­flow­ers mid-century.

My hot take on this is that the reuni­fi­ca­tion work of the ear­ly 20th cen­tu­ry gave Quak­ers a sol­id iden­ti­ty and coher­ent struc­ture. Howard Brinton’s Friends for 300 Years from 1952 is a remark­ably con­fi­dent doc­u­ment. In many areas, Friends became a socially-progressive, par­tic­i­pa­to­ry reli­gious move­ment that was attrac­tive to peo­ple tired of more creedal for­mu­la­tions; mixed-religious par­ents came look­ing for First-day school com­mu­ni­ty for their chil­dren. Quak­ers’ social jus­tice work was very vis­i­ble and attract­ed a num­ber of new peo­ple dur­ing the anti­war 1960s³ and the alter­na­tive com­mu­ni­ty groundswell of the 1970s. These var­i­ous new­com­ers off­set the decline of what we might call “eth­nic” Friends in rur­al meet­ings through this period.

That mag­ic bal­ance of Quak­er cul­ture match­ing the zeit­geist of reli­gious seek­ers dis­ap­peared some­where back in the 1980s. We aren’t on fore­front of any cur­rent spir­i­tu­al trends. While there are bright spots and excep­tions ⁴, we’ve large­ly strug­gled with retain­ing new­com­ers in recent years. We’re los­ing our elders more quick­ly than we’re bring­ing in new peo­ple, hence the forty per­cent drop since the high water of 1987. The small 2017 uptick might be a good sign⁵ or it may be a sta­tis­ti­cal phan­tom.⁶ I’ll be curi­ous to see what the next cen­sus brings.

2023 Update: I seem to have mixed up some num­bers in my orig­i­nal 2018 post and have cor­rect­ed them above.