The default font in Adobe Illustrator CC is Myriad Pro. The default font is selected in the Font menu, Character palette, and as the Normal Character Style in the Character Styles panel. The default font is selected even if the document you open doesn't contain that font or if you last used another font before quitting Illustrator. You can change the default font in Illustrator by editing the default template files.
1. Choose File > Open.
2. Navigate to the following location:
OSDisk\Users\<username>\AppData\Roaming\Adobe\Adobe Illustrator <version number> Settings\en_US\x64\New Document Profiles
It might be easier if you copy/paste this C:\Users\<username>\AppData\Roaming\Adobe\ then change the bolded text and navigate to the version of Illustrator you are using.
Replace <username> with your account name.
Replace <version number> with the following values, depending on the version of Illustrator that you have installed on your system. For more information, see Replace Illustrator version number.
3. Choose the desired default document profile template and click Open.
4. Choose Window > Type > Character Styles.
5. Double-click Normal Character Style in the Character Styles panel.
6. Select Basic Character Formats on the left of the Character Style Options dialog.
7. Choose the desired font from the Font Family menu. You can also change other settings, such as Font Style and Size.
8. Click OK.
9. Choose File > Save As to overwrite the original document profile template and close the file.
10. Choose File > New and select the desired default document profile template.
11. While you are doing this - you might as well update all the files that are in the \New Document Profiles folder to your desired font choice - I have different choices on the Art & Illustration. ai, Film & Video. ai, Mobile. ai, Print. ai, and Web. ai documents.