Site-to-site VPN - How to control LAN access on one end

[cobrahead]

I have a site-to-site VPN (OpenVPN) tunnel connecting two remote locations. Both locations are behind a pfSense box. How do I limit access to the VPN tunnel at one end. ie: I just want IPs 172.16.0.200 - 172.16.0.210 to have access.

[viragomann]

So you may already have assigned interfaces to the OpenVPN instances on both sides. Deactivate all firewall rules on the OpenVPN tabs if you don't need them for other purposes and add rules to your VPN interfaces with limited access.
Remember that the OpenVPN tab is handled as an interface group including all OpenVPN instances running on pfSense.
For the IP range 172.16.0.200 - 172.16.0.210 in your example you can add an alias and use this in the filter rule as source.