Ottawa is the county seat of Putnam County, Ohio. Residents named the town, which was founded in 1833, in honor of the Ottawa people, who once had a village at the site of modern-day Ottawa. Kalida was Putnam County's original seat of government, but a fire destroyed the courthouse in 1866. A county-wide vote by Putnam County residents decided to move the seat of government to Ottawa.
Ottawa became a major meeting place for farmers in the surrounding countryside. The railroad through the community gave farmers access to markets across the United States. Most local businesses either provided services or products for the farmers in the surrounding countryside. In 1886, Ottawa's largest employer, Rice, Brown & Company, employed thirty-nine people. The company produced wagon and carriage wheels. That same year, the town included three newspapers, four churches, and two banks. In 1880, Ottawa's population was 1,293 people, with forty percent of the residents being school-aged children.
Putnam County residents remained committed to agriculture throughout the twentieth century. In 2000, approximately ninety-three percent of the county's acreage was under cultivation. Today, the town's largest employers are in the construction field, with retail establishments following closely behind. Ottawa was the largest community in Putnam County in 2000, with a population of 4,367 people.