Polly is probably Elizabeth Miller's sister.
Had a large family by 1840:
Name: William Robling
Home in 1840 (City, County, State): Pike, Indiana
Free White Persons - Males - Under 5: 1
Free White Persons - Males - 5 thru 9: 1
Free White Persons - Males - 10 thru 14: 1
Free White Persons - Males - 15 thru 19: 2
Free White Persons - Males - 40 thru 49: 1
Free White Persons - Females - 5 thru 9: 1
Free White Persons - Females - 10 thru 14: 2
Free White Persons - Females - 15 thru 19: 1
Free White Persons - Females - 40 thru 49: 1