In the 1860 US Census for Clyman, Dodge County, Wisconsin Isaac D. Barnum, age 31, was enumerated with the family of Harman Isham, whose 19-year-old daughter Joanna he was soon to marry:
Dwelling #224; Family #224
Harman Isham, 49, M, Farmer, Real property $4,000, Personal property $500, b. Vermont
Clarissa Isham, 46, F, b. Vermont
C. S. Isham, 20, M, b. Vermont
Joanna Isham, 19, F, b. Vermont
I. D. Barnum, 31, M, Farmer, Real property $2,000, Personal property $400, b. New York
O. B. Isham, 9, M, b. New York, Attended school within the year
Clarissa Isham, 7, F, b. Vermont, Attended school within the year
In the 1870 US Census for Walnut, Appanoose County, Iowa the family of Isaac D. Barnum was enumerated as follows:
Dwelling #55; Family #56
Barnum, Isaac D.; 40; M; W; Farmer; Real property $2,500; Personal property $549; b. New York; Male citizen of the US of 21 years of age and upwards
Barnum, Joanna M.; 28; F; W; Keeping house; b. Vermont
Barnum, Edwin D.; 9; M; W; b. Wisconsin; Attended school within the year
Barnum, Mary E.; 3; F; W; b. Wisconsin
In the 1880 US Census for District 112, Amsterdam, Hancock County, Iowa the family of Isaac D. Barnum was enumerated as follows:
Dwelling #9; Family #9
Barnum, Isaac; W; M; 51; Head; Married; Farmer; b. New York; Father b. New York; Mother b. Connecticut
Barnum, Joanna; W; F; 39; Wife; Married; keeping house; b. Vermont; Both parents b. Vermont
Barnum, Edwin; W; M; 19; Son; Single; Attended school within the census year; b. Wisconsin; Father b. New York; Mother b. Vermont
Barnum, Mary; W; F; 13; Daughter; Single; Attended school within the census year; b. Wisconsin; Father b. New York; Mother b. Vermont
Barnum, Charles; W; M; 5; Son; Single; b. Michigan; Father b. New York; Mother b. Vermont
Barnum, Albert; W; M; 1; Son; Single; b. Iowa; Father b. New York; Mother b. Vermont
Knowlton, Bruce; W; M; 28; Boarder; Married; Farmer; b. Michigan; Both parents b. New England
Isaac was also reported in the 1885 Iowa State Census, living in Twin Lake, Hancock County, Northeast 1/4 of Section 27, Range 24