Built on a shelf of oneota dolomite limestone, Ottawa was platted in 1853 and became home to a collection of limestone structures built between 1859 and 1875 that reflected strong local craftsmanship and ashlar construction using stone quarried by township landowners with simple tools and methods. Once a group of seven simple, locally crafted structures, now reduced to six, these buildings are listed on the National Register of Historic Places and on Minnesota's Preservation Alliance's Most Endangered Properties list. The Patten farm house, built in 1863 for the David Patten family, who came from Canada in 1855, later belonged to a sand mining corporation after 1986 and was demolished in 2002 for additional mining. Ottawa's Town Hall, built in 1868, first served as a general store owned by Charles Needham and David Patten, was fully acquired by Needham in 1878, and was bought by the township in 1902 for use as a town hall, a role it still serves. The Methodist Church, thought to have been built in 1859, was a simple one-room church with a gable roof and a wood-shingled tower with belfry and spire. The Rinshed House, a story-and-a-half stone cottage at Sumner and Whittier Streets, was built by stonemason John Rinshed, who owned one of Ottawa's seven stone quarries in the 1870s. Trinity Lutheran Church, built by the community from 1865 to 1868, was an example of coursed ashlar construction; after declining attendance, it was sold in 1907 to the Catholic Church as St. Mary's, a mission of St. Anne's in LeSueur, and around 1914 it was sold again, remodeled, and turned into a residence. One-half mile north of Ottawa, German-born Charles Schwartz built a limestone barn in 1874 and a farmhouse in 1875 on his farm. Together these structures reflect both the region's limestone building tradition and the broader struggles of indigenous people and pioneering immigrant families to make homes in the Minnesota River Valley.