“The situation is very tense,” Mayor David J. Berger said. “Serious threats have been made. People are starting to carry weapons to protect themselves.”

Surrounded by farm country known for its German Catholic roots and conservative politics, Lima is the only city in the immediate area with a significant African-American population. Black families, including Mr. Manley’s, came to Lima in the 1940s and ’50s for jobs at what is now the Husky Energy Lima Refinery and other factories along the city’s southern border. Blacks make up 27 percent of the city’s 38,000 people, Mr. Berger said.

Many blacks still live downwind from the refinery. Many whites on the police force commute from nearby farm towns, where a black face is about as common as a twisty road. Of Lima’s 77 police officers, two are African-American.

“If I have any frustration when I retire, it’ll be that I wasn’t able to bring more racial balance to the police force,” said Chief Garlock, who joined the force in 1971 and has been chief for 11 years.

Tarika Wilson had six children, ages 8 to 1. They were fathered by five men, all of whom dealt drugs, said Darla Jennings, Ms. Wilson’s mother. But Ms. Wilson never took drugs nor allowed them to be sold from her house, said Tania Wilson, her sister.

“She took great care of those kids, without much help from the fathers, and the community respected her for that,” said Ms. Wilson’s uncle, John Austin.

Image Residents of Lima, Ohio, posted a sign at the house where Ms. Wilson, 26, was killed and her 14-month-old son was injured. Credit... J. D. Pooley for The New York Times

Tarika Wilson’s companion, Mr. Terry, was the subject of a long-term drug investigation, Chief Garlock said, but Ms. Wilson was never a suspect.