Denmark international Harder, who was sidelined through injury between November and April this season, tweeted: “It’s been a dream coming true playing for this amazing club and I’ve loved every single moment along the way.”
Eriksson and Harder, 30, have both been linked with a move to German side Bayern Munich this summer.
Sweden defender Eriksson has been Chelsea’s captain since 2019 and manager Emma Hayes said she would “forever remain a legend” at the club.
“There are not enough words to describe the impact Magda has had, not just on this football club but on me,” Hayes said.
“She has been a wonderful leader, someone who has helped drive the team and its standards to the levels that we’re at.
“Chelsea will always be her club, it will always be her home.”
Meanwhile, Hayes called Harder, who has scored 44 goals in 79 games for the Blues, “one of the best attacking players in the world”.
Chelsea have two games remaining in the Women’s Super League and are challenging for a fourth consecutive title, having already won this season’s FA Cup – their third in a row – by beating Manchester United 1-0 in the final on Sunday.
Blues midfielder Fran Kirby said on Twitter: “We lose a legend, a captain, someone who gives 100% for the badge and an amazing person. Thank you for everything Magda Eriksson. We will all miss you.”