https://metrics.torproject.org/bubbles.html#country
>requires Java Script
84 countries with 6676 relays (3464 visible)
Germany, US, Netherlands, France are the largest pools of relays.

https://metrics.torproject.org/bubbles.html#country-exits-only

58 countries with 908 exits (776 visible)

It would be nice if this page displayed point counts by country circle. But estimating by the size of the circles about 1/8th of world relays are in USA, and 1/5th of world exits are in USA.

US relays 6676/8 = 834.5 ~ 835
US Exits 908/5 = 181.6~182

So if all 3 nodes in your path stay in the United States, you have 835 C2 * 182 possible paths. this is 63,371,490 or 64 million If you are under surveillance as then only 835*182 = 151,970 possible paths need to be investigated. This is an extremely tractable problem.