Anyone notice that ILL had the most episodes in Season 1, and almost every year there were less episodes.
Season 1 had 36 episodes.
The final 2 seasons had 26 and 27 episodes.
I thought that might only be for ILL, since I'm not familiar with other 50's shows.

I recently started watching the Western The Rifleman.
Season 1 (1958-59) had 40 episodes. They also cut down on episodes every year.
By the final season 5, they were down to 26 episodes.

Was this the norm for 50's shows?

I think Lassie also had a very high number of early eps. Pretty common to see the count dwindle.

This probably has to do with the biggest hit shows becoming more expensive to produce, due to the stars demanding higher salaries, or more time off. The same thing happened in the '60s with The Lucy Show: S1: 30 episodes; S2: 28 episodes; S3: 26 episodes; S4: 26 episodes; S5: 22 episodes plus "Lucy in London" special; S6: 24 episodes.

While 30 plus episodes a season was typical in the '50s and '60s for most shows, by the 70s, 24 episodes a season was standard for CBS sitcoms, and the other two networks produced a similar number. In the 80s, that number dwindled a bit to 22 episodes.

As for 50s shows, it was typical for most shows to produce well above 30 episodes per season. Leave It to Beaver, for example, cranked out 39 episodes each of its six seasons. Of course, during its original run, although it was very popular, it was never a megahit like I Love Lucy. It seems to have gained more popularity in reruns. The Burns and Allen Show was particularly prolific, cranking out 40 episodes most seasons. In its 7th season, they produced 43 episodes! Poor George and Gracie must have been plenty tired! It's no wonder Gracie, with her health problems, had to quit the show.