Unless stated otherwise numbers are for Christians in America.

By decade:


Five Key Findings on Religion in the U.S. Gallup

By age:

The number who attend services at least weekly or nearly every week in 2010:
Generation         Born            Age     Attendance
Millenials 1981-2000  18-29  18-27%
Gen X      1965-1990  30-45  27-33%
Boomer     1946-1964  46-64  32-38%
Silent     1928-1945  65-82  44-48%
Greatest   before 1928   83+ 56-60% 
Note these numbers vary depending on which report you look at.
The numbers above, from Religion Among the Millennials | Pew Research 2010, tend to be in the middle.

By Religion

Religious Beliefs and Practices | Pew Research Center


Various
ABC News/BeliefNet Poll: Religious Services – 2002

 All men          32%
 All women        44
 Catholic men     26
 Catholic women   49
 Protestant men   42
 Protestant women 50

By Location:
Church attendance - Wikipedia

By State:
Percentage of Christians who attend church at least once a week, 2014
Rank State Atten-
dance
2016
Election
1 Utah 70% R
2 Tennessee 59% R
3 South Carolina 57% R
4 Virginia 57% D
5 Alabama 55% R
6 Mississippi 54% R
7 West Virginia 54% R
8 Louisiana 53% R
9 Oklahoma 53% R
10 Wyoming 52% R
11 Georgia 51% R
12 Nebraska 51% R
13 Texas 51% R
14 Arkansas 50% R
15 Kentucky 50% R
16 North Carolina 50% R
17 Idaho 49% R
18 Indiana 49% R
19 Ohio 49% R
20 Arizona 48% R
21 Iowa 47% R
22 Kansas 47% R
23 Missouri 47% R
24 Florida 46% R
25 Montana 46% R
26 Rhode Island 46% D
27 California 45% D
28 Delaware 45% D
29 Michigan 45% R
30 Nevada 45% D
31 Washington 45% D
32 Illinois 44% D
33 New Mexico 44% D
34 Oregon 44% D
35 Pennsylvania 44% R
36 South Dakota 44% R
37 Alaska 43% R
38 Minnesota 43% D
39 Colorado 43% D
40 New York 43% D
41 Maryland 42% D
42 New Jersey 42% D
43 North Dakota 41% R
44 Hawaii 40% D
45 Washington, D.C. 39% D
46 Wisconsin 38% R
47 Connecticut 36% D
48 Massachusetts 34% D
49 New Hampshire 34% D
50 Vermont 34% D
51 Maine 31% D


By Country
Percentage of Christians who attend church at least once a week. (2008-2009) The following attendance statistics are mostly based on self-reporting surveys and may not accurately reflect real attendance figures.
Nigeria87%
Zambia85%
Chad83%
Ghana82%
Liberia82%
Tanzania82%
Mozambique81%
Uganda81%
Kenya80%
Guatemala78%
Ethiopia75%
Rwanda75%
Democratic-Republic-of-the-Congo72%
Cameroon70%
Honduras70%
El Salvador68%
Guinea-Bissau66%
Botswana62%
South-Africa62%
Nicaragua58%
Philippines58%
Malta57%
Dominican-Republic56%
Bolivia55%
Costa Rica55%
Colombia52%
Republic-of-Ireland51%
Panama51%
Morocco50%
Brazil49%
Poland48%
Mexico47%
United-States47%
Ecuador39%
Israel38%
Italy37%
Lebanon37%
Peru35%
Paraguay33%
Canada29%
Greece27%
Slovakia26%
Venezuela26%
Australia25%
Argentina22%
Chile22%
United-Kingdom20%
Spain19%
Uruguay16%
Germany13%
Ukraine13%
Lithuania12%
Belgium11%
France11%
Russia8%

Links:
America's Changing Religious Identity | PRRI