How many CR 30 monsters are in the D&D 5e SRD?

1 CR 30 monsters appear in the SRD 5.2.1 — Tarrasque.

How much XP is a CR 30 monster worth?

A CR 30 monster is worth 155,000 XP per the SRD's Experience Points by Challenge Rating table.

D&D 5e SRD · Challenge Rating

CR 30 monsters

1 monster at Challenge Rating 30 — worth 155,000 XP each (155,000 XP combined). Click into any of them to roll attacks, damage, and saves straight from the stat block.

Name	Type	Size	HP	AC
Tarrasque	Monstrosity (Titan)	Gargantuan	697	25

Stat blocks from the System Reference Document 5.2.1 © Wizards of the Coast LLC, used under the Creative Commons Attribution 4.0 license.