Sanborn Fire Insurance maps of Ottawa can be found at http://luna.ku.edu:8180/luna/servlet/kuluna01kui~12~12. Type in Ottawa in the Search box at the top right of the page. KU has them for 1884, 1888, 1893, 1899, 1905, and 1912. Franklin County Historical Society has a few others.
Explore Kansas in 329 digitized maps in the Special Collections of Wichita State University Libraries at http://specialcollections.wichita.edu/collections/maps/index.asp. The maps date from 1556-1900. Click progressively on the Franklin County area, for instance, to zoom in.