as of the end of; making ... the last
Used with time expressions (today, this month, this year, etc.) to indicate that something ends or will be the last occurrence. Often implies a finality or a cutoff point.
We will close as of today.
I will retire at the end of this month.
をもって is a formal way to indicate a point in time when something happens or ends, similar to を限りに but without the strong nuance of 'last' or 'final'.
Composed of the particle を, the noun 限り (limit, as far as), and the particle に. The expression literally means 'with ... as the limit' and has developed the idiomatic sense of marking a final point in time.