www.nhdeeds.com
Rockingham County's Registry of Deeds has an online search tool for deeds going back to 1629. Hampton, New Hampshire is in Rockingham County.
Here's the link to the page where you start your search process.
http://www.nhdeeds.com/rockingham/RoDisclaimer.html
You'll have to click on the disclaimer link, and then start a Java applet. Which means you'll have to use another browser besides Chrome or Edge, Try using Internet Explorer, that browser still powers Java.
You'll find a lot of Cass related deeds in Hampton after the 1680's. Strangely no Cass deeds before that time, there are earlier deeds in the Essex County index for Massachusetts.
For a period, parts of New Hampshire, specifically Old Norfolk County, was in of Massachusetts Bay Colony.
I'd like to discover who was deeded the old farm that is now located in Seabrook? That's the farm owned by the Rev. John Wheelwright, and sold to John Casse in 1664. John sold part of the farm to Thomas Philbrick jr. In 1680 the farm was inherited by Joseph & Samuel Cass.