The Church of Jesus Christ of Latter-day Saints (the "Mormon" church) does not release membership statistics by city, the smallest area they have statistics for is by state.
Typically, the southern and eastern parts of Idaho have more Mormons than the north and western portions.
As of January 1, 2012, the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) reported 417,002 baptized members in the state of Idaho. In 2011, the population of Idaho was reported to be 1,584,985. This means that about 28% of the population of Idaho is Mormon.
The Church of Jesus Christ of Latter-day Saints (the "Mormon" church) does not release membership statistics for an area smaller than a state, so it is impossible to know the exact Mormon population of a city or town. However, there are many small towns in Utah in which 95-100% of the population are baptized Mormons.
Boise
The smallest city in Idaho is Rockford, with a population of around 320 residents. It is located in Bonner County in the northern part of the state.
Boise, Idaho is the only city in Idaho with a population over 100,000.http://www.citypopulation.de/USA-Idaho.html
There are about 175,000 baptized members of the Church of Jesus Christ of Latter-day Saints (the 'Mormon' church) in Nevada. This means about 6% of Nevada residents are Mormon.
Idaho City, Idaho, is located approximatly 23 miles N/NE of Boise on Idaho Route 21. Population is roughly 500. (See Google Maps)
The Church of Jesus Christ of Latter-day Saints (the "Mormon" church) does not release membership statistics for cities, only for states. So we don't know exact the Mormon population of Salt Lake City in 2004, but it was probably around 30-40%. The city itself has quite a low Mormon population compared to the rest of the state.
According to the 2000 US Census the population is 76.
Ketchum is a city in Blaine County, Idaho. It is located in the central part of Idaho. The population was 2,689 at the 2010 census.
Paris, France. Paris in Idaho is located in the county of Bear Lake and has an average population of 513.
The population of the city was 205,671 residents in the 2010 US Census.