If my church was collecting for our missionary and I made out a check to the church with the missionary family name in the memo line, is this tax deductible?

[TomK · Accepted solution]

If you made the check out to the church, then yes.  If the check is made out to an individual, then it's not deductible.

"You can't deduct contributions to specific individuals, including the following. 

Contributions to individuals who are needy or worthy. You can't deduct these contributions even if you make them to a qualified organization for the benefit of a specific person. But you can deduct a contribution to a qualified organization that helps needy or worthy individuals if you don't indicate that your contribution is for a specific person. Example. You can deduct contributions to a qualified organization for flood relief, hurricane relief, or other disaster relief. However, you cannot deduct contributions earmarked for relief of a particular individual or family. 

Payments to a member of the clergy that can be spent as he or she wishes, such as for personal expenses. Expenses you paid for another person who provided services to a qualified organization. Example. Your son does missionary work. You pay his expenses. You can't claim a deduction for your son's unreimbursed expenses related to his contribution of services."

IRS Pub. 526 - Charitable Organizations (pg. 6): https://www.irs.gov/pub/irs-pdf/p526.pdf

[Opus 17]

Memo fields on checks are generally non-binding.  Unless you had a written contract with the church that your money could only be spent on the missionary, then it is a donation to the church.