Captain reported similar sounding fixes; HYVAL and HIVAL; resulted in a clearance deviation.

Narrative

While copying my Clearence I misspelled my first waypoint 'Hyval' I spelled the first fix 'hival' which is in Texas.After departure; I contacted Big Sky Departure. Big Sky Departure cleared me to Hyval. I proceeded direct to Hival which is in Texas. Departure queried 'where are you going'? and that I should be direct Hyval. I looked down at the fix I was navigating to; and initially wasn't sure what was wrong; then realized the possibility of an incorrect spelling; so I zoomed out on my Multifunction Flight Display (MFD) and realized I imputed the wrong spelling of the fix. I then asked Departure for the correct spelling of the fix; and while giving the correct spelling gave me a heading for vectors to the fix. Correction in reviewing assigned clearances. After inputting clearance; review route and fixes for proper spelling and known positions. If I would have reviewed my clearance; on the flight plan page and MFD; I would have seen that the location 'Hival' was in the incorrect position in my assigned routing; and that the spelling was incorrect.