You can customize your site’s footer widget area font and copyright section font from
Dashboard >> Appearance >> Customize > Footer
Scroll down below other options and you will find section to change the font of your site footer
Widget Title
This setting lets you change the font family, size, line-height and text transform of the footer widget title.
Widget Content
This settings lets you change the font family, size, line-height and text transform of all the content in your footer widgets.
Copyright Section
This settings lets you change the font family, size, line-height and text transform of the copyright text on your site site’s footer area.