The organization provides food, clothing, drug rehabilitation and medical services to the city's poor and homeless, including seniors, disabled persons and veterans.
"And they are able to eat because people step forward to help them," St. Anthony Foundation spokeswoman Francis Aviani said.
Aviani said today's milestone illustrates the organization's tradition of sustainability just in time for Earth Day.
She said the foundation serves about 2,600 meals each day of the year. Roughly three-quarters of the food is reclaimed, from second-harvest fruits and vegetables with minor imperfections to day-old baked goods, all of which would otherwise be thrown out.
The foundation also recycles food scraps and unfinished meals, some of which is used as compost for local farms.
"So we're a pretty sustainable organization in general," Aviani said.
Aviani expects the 36 millionth meal to be served at lunch today. The foundation, which began serving free meals in 1950, tallies each one, she said.
"We actually have a counter that counts every tray that walks by," she said.
Today's meal of chicken, pasta, salad and dinner rolls will be marked by a blessing and a celebratory cake.
"On one hand, that's a lot of meals and that tells you that a lot of people are hungry," Aviani said. "On the other hand, that tells you that a lot of people are stepping forward, every day, 365 days a year, to make sure that hungry people can be fed."