Yes, nonillion is a real number. It is a term used in the English-speaking world to denote a very large number. The value of a nonillion can vary depending on the numbering system used.
In the short scale system, which is commonly used in the United States and modern British English, a nonillion is equal to 1030. This means it is a 1 followed by 30 zeros:
1,000,000,000,000,000,000,000,000,000,000
In the long scale system, which is used in some European countries, a nonillion is equal to 1054. This means it is a 1 followed by 54 zeros:
1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
So, whether nonillion is 1030 or 1054 depends on the numbering system you are using. Both are valid and represent extremely large numbers.