Cole has become a style icon as her star has soared in the last year.
"The world has gone completely insane for our Cheryl," the Telegraph quoted Tatler, as saying.
Elettra Rossellini came second while Caroline Sieber landed the third spot.
Kate Moss, last year's number two, and fellow supermodel Agyness Deyn, who was at number 10 last year, failed to make the top 10, compiled by the magazine.
Georgia May Jagger stood fourth and Marie-Chantal of Greece rounded off the top five.
Here is Tatler's top 10 "best dressed" list for 2009:
1. Cheryl Cole
2. Elettra Rossellini
3. Caroline Sieber
4. Georgia May Jagger
5. Marie-Chantal of Greece
6. Alice Dellal
7. Leigh Lezark
8. Natalie Portman
9. Claudia Schiffer
10. Emma Watson (ANI)