Because your militia in Manor Lords draws from the actual number of families in your village, it can be difficult to maintain a persistently strong force. To better protect yourself, you can hire mercenaries, and this is how that is done.
While playing Manor Lords, you’re going to see notifications about mercenaries rather frequently – about once a month. Available mercenaries work on a rotation, so you won’t always have the option to choose from the same ones.
To hire a mercenary group, you need to select the military menu on the taskbar. You then need to select the new unit button (the big “+” sign next to your existing units.) From there, you’ll be given options for the new unit you want to create. On the right-hand side of the menu is the option to recruit mercenaries. Clicking on it will show you the mercenary group currently available, as well as the cost.
The cost for mercenary groups comes from your treasury, and the only way to get funds into the treasury is through taxes. At the time of writing, the only tax that does this is Land Tax, as Tithes get you influence, and the other possible taxes are still in development. The Mercenary Tax would be especially helpful since it would cover the hiring of mercenary units and wouldn’t harm your approval so long as you were actually using the funds for that purpose, but for now, you can only use land tax to hire and pay them, and that will harm your approval.
To note, you will need to continually pay them upfront each month so you will continually need the money available in the treasury.
When you hire a mercenary unit, they will enter the map from the edge, but not necessarily in your territory. Once again, this is how it is at the time of writing, but I hired a mercenary group and they wandered in from the opposite end of the map, far away from my controlled regions. You may need to zoom out to the regional map to look for the red unit crests, then have them walk to where you need them.