Smedinghoff was being remembered for her "quiet intelligence" and being calm in any and all situations.
Her former teachers at Fenwick celebrated her life. Her Spanish teacher and International Relations Club monitor Irene Drago praised Smedinghoff's willingness to help others.
Hundreds of students also attended the Mass. Most never knew Smedinghoff, but some might have met the 2005 graduate when she made a visit to the school two months ago.
Smedinghoff was killed while she was delivering text books to school children in southern Afghanistan. A suicide bomber struck the vehicle she was in.
Smedinghoff entered the foreign service after graduating from Johns Hopkins University. She grew up in suburban River Forest, Ill., attended St. Luke's Catholic Church.
She is survived by her parents and three siblings who also attended Fenwick High School.
On Monday, the young woman's parents, Tom and Mary Beth Smedinghoff, said while they missed their daughter, she died doing what she loved.
"Anne lived a very full live. She encouraged others to embrace each day," said Mary Beth Smedinghoff.
"[We are] immensely proud," father Tom Smedinghoff said. "We could not be prouder of Anne and of the work that she was doing. That is one of the things that gives us comfort."
Also Monday, Sen. Dick Durbin paid tribute to Smedinghoff on the U.S. Senate floor.
"Our civilians serving abroad can face a variety of threats. Yet, they do so with dedication, patriotism, and a belief that the United States can be a voice for good in the world. Sadly, today I come here with a heavy heart, as the life of one of the brightest young officers from my home state of Illinois was cut short on Saturday in one of those dangerous places," Durbin said. "I know my colleagues join me in our heartfelt condolences to her family, and in our ongoing appreciation for the sacrifices made by our diplomatic corps."
The state department employee had been a diplomat for three years and had also worked in Venezuela after college.
Sec. of State John Kerry met Smedinghoff for the first time last month.
"Anne was everything that was right about our foreign service. She was someone who worked hard so that others could live a better life," Kerry said.
Smedinghoff is being remembered in the Oak Park community with white ribbons and flags donated by church members.
Her sister, brother and aunt attended Tuesday's memorial but asked that the media respect their privacy. They did not make any public comments.