SB :

1) Theodore Crowell's Marriage Certificate

2) Universalist Church Cemetery Records

3) Barnstable Vital Records

4) 1840 U.S. Federal Census

5) FamilySearch™ International Genealogical Index v5.0

Unknown:

Notes :

I found a records of "Leander Crowell or Furnell" on LDS listing a corresponding date of birth.  Only a mother, Nabby Furnell is listed, no father.  Was his mother not married when he was born?  I also found a record for Abigail Furnell, born 1790 in Yarmouth, Barnstable, parents Benjamin and Hannah, but no other information.  There is also a record in the book of Massachusetts Name Changes dated April 1839 showing Leander Crowell Furnell being granted the right to change his name to Leander Crowell.