The Social Welfare Board was founded by Dr. C. Daniel Morton, to help the people in Buchanan County and St. Joseph.
The clinic includes primary health care, dental, women's health and a holistic health care clinic for the homeless.
It is the oldest free clinic in the United States, and has served thousands of residents throughout its history.
"I am impressed with the versatility and the stick-with-it of the clinic, and how they've done what they've done over the last 100 years," said Dr. John Nelson.
"For something to be able to last that long and sustain itself through gosh, all sorts of economic times. Recession, depression, you know, it's just amazing," said Linda Judah.
The clinic is asking patients to give back by donating, writing a thank-you note, completing a survey, sharing their story, or developing a health care plan to motivate others.