“She was proof that one voice that keeps on ringing, singing, praying and speaking can make a difference,” the statement said.

Other tributes poured in online, including from C. Denise Marcelle, a state representative.

“This woman was amazing and loved her history,” she wrote on Sunday. “She never bothered anyone, just wanted to expand her African American Museum downtown, where she continually hosted the Juneteenth Celebration yearly. I loved working with her and am saddened by her death.”

By Monday, Ms. Marcelle said on Facebook that her sadness had turned to anger. She called on the community to take action by donating to the museum.

“It’s not enough that we talk about her infectious smile, nice demeanor or knowledge she possessed about our history,” she wrote. “Let’s make sure that her museum is kept open and expanded for our future generations.”

Ms. Roberts-Joseph's body was found in a part of town between her home and the museum.

“The community is in uproar,” Dr. Rani Whitfield, a local doctor who is running for coroner, said in an interview Monday. He posted an online tribute to Ms. Roberts-Joseph, praising her community work and Juneteenth celebrations.

“Seventy-five years old, that is unacceptable,” he said. “I am devastated by this.”

Residents in Baton Rouge were consumed over the weekend by Tropical Storm Barry, which had threatened catastrophic fatal flooding but in the end did not deliver on that worst case. But Dr. Whitfield said many people were equally upset at the news of Ms. Roberts-Joseph’s death.

“It seemed to be just as important to the community as the flood,” he said.

In an interview with The Advocate, her sister, Beatrice Johnson, who lives nearby, said that she had seen her sister daily, including on Friday.