The previous record fees exceeded 685,000 pounds, when Bay Fc Racheal Kundananji fell last February.
Chelsea set the record for the British transition at the signature of Mayra Ramirez for 384,000 pounds in January 2024.
It was not the first Chelsea signature on the transfer window in January after they fought from the competition from Lyon.
Chelsea made her a priority goal after losing defender Kadisha Boucanan for a knee injury at the end of the season.
“Naomi is a world -class global defender who will now come in the early years of her career,” said Paul Green Football President Naomi.
“Ringing its composure to the ball, the ability to read the game, along with its pace and sports, will add high quality to a very talented team.
“She is undoubtedly ready for this next step in her career and we are happy that she will be with Chelsea.”
In 2023, San Diego helped win the National Women's Football League shield (NWSL) and was appointed the best American football player.
It was part of the USA team that won gold in the 2024 Olympics in Paris.
