He was also known as Squire Blanch Duncan.

1850 census of Floyd Co., Virginia, district 15, enumerated 30 Aug, lists on p. 103 as family #746:
Blanch Dunkin, 41, farmer; Catherine, 37; James C., 16; Mary S., 14; Martha, 12; Solomon, 11; Susan, 10; Jacob, 9; Blanch, 7; Reed, 6; Andrew, 4; Greenberry, 2; Robert, 4/12. All born in Floyd Co. (this is one of the censuses that recorded counties for births in Virginia.)

The son recorded here as Jacob age 9 is recorded in later records as John Tobias Duncan.

The next household is headed by Samuel Dunkan age 38.

1860 census of Floyd Co., Virginia, Copper Valley P.O., enumerated 26 July, lists on p. 121 as family #866/813:
Blanch Duncan, 50, farmer; Catharine, 46; Jas C., 27; Mary S., 25; Martha J., 23; Solomon, 21; Susanah, 20; John, 18; Blanch, 15; Reed, 13; Andrew J., 11; Greenberry, 10; Robert, 9; Artemas (male), 8; Catharine, 6; Rachail, 5; Ruth, 2 1/12; infant male, 2/12. All born in Virginia.

Note that there is a substantial age shift for Blanch Jr. though Greenberry. The 1850 census is probably closer to correct.

1870 census of Floyd Co., Virginia, Indian Valley district, enumerated 13 Aug, lists on p. 2 as family #6:
Duncan, Blanch, 62, farmer; Catharine, 58; Greenberry, 21; Artemus (male), 18; Catherine, 15; Rachel, 14; Ruth, 12; Bluford, 10. All born in Virginia.

The next household is headed by their son Solomon (his brother John is living with him), the one after that by their son Robert, the one after that by their son Andrew, and the one after that by their son Reed.

1880 census of Floyd Co., Virginia, Indian Valley district, enumerated 18 June, lists on p. 37 as family #314/318:
Duncan, Catharine, 65, widowed, keeping house; Beauford, son, 20, single, farmer. Both born Va Va Va.

The preceding household is headed by Blanch and Catharine’s son John, and the one before that by their son Solomon.