thePeerage.com

[col48]

Cracroft's peerage has the following entry for him.

You have to look under George the 1st Marquess (& 4th Viscount), his father, where he appears as the first child.

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Lord George Townshend, later 16th Baron Ferrers of Chartley and 8th Baron Compton later [b]1st Earl of Leicester[/b] later 2nd Marquess Townshend
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So he was [i]also[/i] Earl of Leicester.

Wikipedia has this creation as 1784, quoting the London Gazette of 8 May 1784.

He was succeeded as Earl by his son, George (234117) and the title was extinct on his death.

I suppose that the fact that the son was still living in 1837 when Thomas William Coke was made E of L explains why TC was 'Earl of Leicester, of Holkham in the County of Norfolk' rather than plain 'Earl of Leicester'.