I did a brief search in the "Lipscomb: 300 Years in America" book. The entire book has been scanned and is available online (though a bit difficult to navigate) in the Online Collection at BYU, here: http://tinyurl.com/e3bnw

Page 171 has a brief blurb about the Kenton Co., KY, census showing Rebecca (Riggs) and Richard, who was possibly the son of Joel (but unconfirmed). The book recommends searching the Kenton County records for further details.

See the pages here (in PDF format):

p. 171: http://tinyurl.com/b2gsq
p. 172: http://tinyurl.com/abqhj
p. 173: http://tinyurl.com/bzxd9
p. 174: http://tinyurl.com/9zbuf
p. 175: http://tinyurl.com/c386m

pages 125-226 (24mb): http://tinyurl.com/9uzce

p. 573 index page showing Rebecca Riggs: http://tinyurl.com/8qko5

[Link addresses shortened with "tinyurl" to prevent them from breaking, since they're long.]