The most extensive collections of Delaware maps are at the University of Delaware Library, the Historical Society of Delaware, and at the Wilmington Institute Free Library.
A valuable atlas that shows names of landowners is:
Beers, Daniel G. Atlas of the State of Delaware. . . Philadelphia, Pennsylvania: Pomeroy and Beers, 1868. (Family History Library fiche 6332689.)
There are United States atlases for the following years with excellent Delaware maps: 1790, 1810, 1823, 1838, 1862, 1878, 1884, and 1917 (Family History Library film 002083.)
The best atlas for showing changes in county formation and boundary disputes is by the:
Newberry Library. Historical Atlas and Chronology of County Boundaries, 1788-1980. Volume 1. John H. Long, ed. Boston, Massachusetts: G.K. Hall & Company, 1984. (Family History Library Ref book 973 E7hL v. 1; fiche 6051426; 3 fiche.)
Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html
United States Census Bureau State and County Map. This map will allow you to zoom in on any state or county in the United States and read the names of all of the neighboring counties.