The 1870 U.S. Federal Census has increased, again, the amount of questions asked.  The questions are becoming more specific and this is when male U.S. Citizenship became a question.

1)  Dwelling-houses numbered in the order of visitation.
2)  Families numbered in the order of visitation.
3)  The Name of every Person whose place of abode on the first day of June, 1870, was in this family.
Description:
4)  Age at last birth-day.  If  under 1 year, give months in fractions, thus 3/12.
5)  Sex – Male (M), Female (F).
6)  Color – White (W); Black (B); Mulatto (M); Chinese (C); Indian (I).
7)  Profession, Occupation, or Trade of each Male Person over 15 years of age.
Value of Real Estate:
8)  Value of Real Estate.
9)  Value of Personal Estate.
10) Place of Birth – Naming the State, Territory, or Country.
Parentage:
11) Father of Foreign born.
12) Mother of Foreign born.
13) If born within the year, state month (Jan, & c.).
14) If married within the year, state month (Jan, & c.).
15) Attended School within the year.
Education:
16) Cannot read.
17) Cannot write.
18) Whether deaf and dumb, blind, insane, idiotic, pauper, or convict.
Constitutional Relations:
19) Male Citizens of U.S. of 21 years of age and upwards.
20) Male Citizens of U.S. of 21 years of age and upwards where rights to vote is denied on other grounds than rebellion or other crime.