Hi jcraft1
This belongs to footer module and you can find the translation for this copyright text in the file:
/language/en-GB/en-GB.mod_footer.ini
MOD_FOOTER_LINE1="Copyright © %date% %sitename%. All Rights Reserved."
MOD_FOOTER_LINE2="<a href="QQ"https://www.joomla.org"QQ">Joomla!</a> is Free Software released under the <a href="QQ"https://www.gnu.org/licenses/gpl-2.0.html"QQ">GNU General Public License.</a>"
To override this, I recommend you to override it via Backend >> Extensions >> Languages >> Overrides >> and add translation for above 2 constants:
MOD_FOOTER_LINE1
MOD_FOOTER_LINE2