Since IE9 doesnt support CSS3 columns, or flexbox, here's an IE9+ method for creating a vertically oriented ordered list that breaks to two columns without needing extra elements, classes, or JS.
All items are absolutely positioned based on the line height using nth-child. The items in the second column are selected with nth-child using a clever trick to select half the items. This overrides the initial absolute position styling. The second columns is staticly positioned and pushed right with margin. I've used Sass to make generating these rules easier but its not required. One caveat is that you'll need to know the maximum number of items that might be held in a single column. It will work for any number of items below that value. In addition, this positioning will only work with items that will fit on a single line.