Missouri's 18th Senatorial District is one of 34 districts in the Missouri Senate. The district has been represented by Republican Cindy O'Laughlin since 2019 and she has served as president pro tempore since 2025.
The district is based in rural northeastern Missouri and includes Adair, Audrain, Clark, Knox, Lewis, Macon, Marion, Monroe, Putnam, Ralls, Randolph, Schuyler, Scotland, and Shelby counties. Major municipalities in the district include Hannibal, Kirksville, Mexico, and Moberly. The district is also home to Truman State University, Mark Twain Lake, and several state parks, forests, and conservation areas.
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