The first Numerical Analysis Day took place in 1983, at the University of Waterloo.
In 1982-83, James (Jim) Varah (Ph.D. graduate of Stanford University, supervised by George Forsythe, then for many years Professor in the Computer Science Department of the University of British Columbia, as well as chair of that department for several years) was visiting the University of Waterloo, and collaborated with J. Alan George (also Ph.D. graduate of Stanford University, supervised by George Forsythe, then for many years Professor in the Computer Science Department of the University of Waterloo, as well as senior administrator, vice-president, provost and Dean of Mathematics) to organize an event of similar nature as those organized by Gene Golub (for many years Professor of Computer Science at Stanford University) at the Bay area.
At that time, all announcements were on real paper.. Since then, the tradition continued with minor gaps, and hopefully will keep going. These events take place late April or May, and often (but not always) a Friday. Here are the schools that organized the NA day:

 1 Waterloo  ? ?   1983      
 2 Toronto  10 Apr 1984 (Tue) announcement Syvert (Paul) Norsett was speaker 
 3 ?
 4 York     14 Apr 1986 (Mon) announcement
 5 Waterloo 29 May 1987       announcement Gene Golub was guest speaker as he was getting an honorary degree the next day
 6 Toronto  22 Apr 1988       announcement Ian Gladwell was guest speaker
 7 Guelph   14 Apr 1989       announcement
 8 ?        18?Apr 1990 (Wed)
 9 Queen's  19 Apr 1991
10 Western   2 May 1992 (Sat)
11 McMaster  1 May 1993 (Sat)
12 Toronto  15 Apr 1994
13 Waterloo 12 May 1995
14 Western  27 Apr 1996 (Sat)
15 Toronto  30 Apr 1997 (Wed)
16 Ryerson   8 May 1998
17 McMaster 29 Apr 1999 (Thu)
18 Western  13 May 2000 (Sat) jointly with 7th East Coast Computer Algebra Day (ECCAD'2000)
19 Waterloo 15 Jun 2001
20 Toronto  19 Apr 2002 -- Fields
21 McMaster  2 May 2002 (Thu)
22 Western   1 May 2004 (Sat)
23 Waterloo 29 Apr 2005
24 Toronto   5 May 2006
25 UOIT      4 May 2007
26 York      9 May 2008
27 Western   8 May 2019
28 Waterloo 14 May 2010
29 McMaster 13 May 2011
30 Toronto  11 May 2012 -- Scarborough
31 UOIT      3 May 2013
32 York     15 May 2014
33 Western   8 May 2015
34 Waterloo 27 May 2016
35 McMaster 19 May 2017
36 Toronto   4 May 2018
37 UOIT      3 May 2019
38 York     27 May 2022
39 Waterloo 19 May 2023
40 McMaster 30 May 2025
41 Toronto   1 May 2026

Many thanks to Tom Fairgrieve for finding announcements of some early NA days and providing interesting information.