Brad Hillis called this data compilation he did to my attention; I haven't verified its accuracy, but the recent (2005-17) data looks roughly right.  Readers can weigh in at Wikipedia to correct the data if need be.  Neither list is adjusted for class size.

Here are the twenty law schools that have produced the most Supreme Court clerks since 1882:

Rank/ Law School/ # clerks / % of all clerks

1) Harvard 607 27%

2) Yale 396 18%

3) Chicago 156 7%

4) Stanford 137 6%

5) Columbia 135 6%

6) Virginia 110 5%

7) Michigan 87 4%

8) Georgetown 61 3%

9) Berkeley 59 3%

10) NYU 54 2%

11) Penn 48

12) Northwestern 42

13) Texas 35

14) GW 26

15) Duke 21

16) UCLA 19

17) Notre Dame-17

18) BYU 13

19) Indiana 11

19) Minnesota-11

And here is Mr. Hillis's list of the top 20 law schools which have produced the most clerks since 2005 through 2017 (again, note that Harvard is more than twice the size of Yale, Stanford, and Chicago; that Virginia, Columbia, and NYU are about twice the size of the latter; etc.):

 

Rank / Law School / # clerks 2005-2017

1 Harvard 124

2 Yale 120

3 Stanford 39

4 Virginia 32

5 Columbia 24

5 Chicago 24

7 NYU 17

8 Georgetown 14

8 Michigan 14

10 Northwestern 10

11 Berkeley 9

11 Duke 9

13 Penn 7

13 GW 7

15 Georgia 6

16 BYU 4

16 Texas 4

16 Notre Dame 4

16 Utah 4

20 Cornell 2

20 Minnesota 2

20 Pepperdine 2

20 Vanderbilt 2