It may be that counting sheep helps some get to sleep, but shepherds count sheep to make sure the little darlings are all present and correct. Not content with "one...two...", shepherds would frequently use Celtic-based numbers:

This counting system was used until recently throughout the North of England to my knowledge (the words shown below are Cumbrian in origin), with variants in other parts of the country, although the custom (or practice) ceased earlier in the South, although I recently heard of the continuing use in Lincolnshire dialects as well.

The numbers are sometimes still heard as a part of skipping songs - in fact, I heard them being sung by children playing in a street in Richmond only about two years ago.

1. Yan
2. Tan
3. Tethera
4. Pethera
5. Pimp
6. Sethera
7. Methera
8. Hovera
9. Covera
10. Dik
11. Ena dix
12. Tena Dix
13. Thethera dix
14. Pethera dix
15. Bumpit
16. Ena bumpit
17. Tena bumpit
18. Tethera bumpit
19. Pethera bumpit
20. Siggit

To some of you, this may look (or sound) rather familiar. In that case, consider this - there is a connection with the Breton language, and they count similarly!

The numbers also form part of the chorus of The Lincolnshire Poacher by The Watersons, on their album Green Fields. Thanks to Gritchka, I can also advise of a play 'Yan Tan Tethera' by Tony Harrison.

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I am not making this up: http://www.traditionalmusic.co.uk/traditional-music/ency/UVWXYZ.htm
http://nauvoo.byu.edu/TheArts/Theater/studypackets/Lesson21/dialect.htm