You can write it either way or even the 26th of May or 26 May.
26th is the ordinal number and twentysixth is the oridnal word
I believe May 26th 1973 was a Friday. We have a son born on May 26th 1971 which I know was a Wednesday.
26th, May, 1951, was a Saturday.
May 26th, 1967 was a Friday.
26th May 1970, was a Tuesday.
May 26th, 1997 fell on a Monday.
May 26th, 1966 fell on a Thursday.
May 26th, 2005 fell on a Thursday.
May 26th, 1974 fell on a Sunday.
May 26, 1900 fell on a Saturday.
I think John Wayne was born on May 26th.
August 26th, 1990 is written as: VIII/XXVI/MCMXC