Paychecks and Reporting

Question: If a pay period ends Dec 31st and the check date is Jan 2nd, is it a check for last year and reported as such?

Answer: According to IRS Publication 15, which covers payroll, the date on the paycheck establishes the period that the check is reported in no matter when the wages are earned. 

In the example given, a Jan 2nd paycheck date and a pay period ending date of Dec 31st would be a January check and would be reported with the January taxes and on the appropriate forms for the period.