To claim a dependent on your taxes, the dependent must be a citizen of the U.S., or a resident of Mexico or Canada. Even though an LDS missionary may be living in another part of the world, the missionary's residency or citizenship does not change. The Internal Revenue Service, or IRS, requires you to fill out the citizenship or residency of any dependents you claim on your tax return.
You must have a qualifying relationship, as defined by the IRS, with an LDS missionary to claim the missionary as a dependent on your tax return. You may claim children, step-children, nieces, nephews, grandchildren, foster children, siblings and step-siblings on your tax return if the dependent and your relationship with them meet all other requirements established by the IRS. If you do not have one of these specific relationships with the missionary, you may not claim the LDS missionary as a dependent on your taxes.
The IRS requires that a person who is claimed as a dependent on another's tax return must not provide more than half of his own support for the tax year. Scholarships and foster care payments do not count as a dependent providing his own support. LDS missionaries do not earn any income while serving a mission, but if a missionary worked for part of the tax year they may have earned enough to not be eligible as a dependent.
The IRS allows you to claim people under a certain age as a dependent. If a person is not attending school full-time, then the person you wish to claim as a dependent cannot have turned 19 before the end of the tax year. If a person is attending school full-time, then you can claim the person as a dependent up to the age of 24. Since LDS missionaries cannot serve until they turn 19 and they do not attend school while serving a mission, you cannot claim a missionary as a dependent on your taxes. You may claim an LDS missionary as a dependent for the previous tax year, as long as he did not turn 19 during that year.