Name ranked no...?

[User2468]

How do you find out how 'popular' a name is/was?

I can only find details of top 100.

DS's name is rare but not unusual and I was curious to see where he ranked, now and when he was born.

I think this might be the link you want:
names.darkgreener.com
If it's a really rare name (less than three a year, iirc) it won't appear.

If your in the U.K., look up the national statistics website. They have every name born in each yr, it's rank and how many babies born with that name.
It's published every September so currently has the list upto 2015.

What they said. This website also takes the ONS info and makes it easier to access www.britishbabynames.com/blog/top-1000-names-in-england-and-wales-2015.html