So we were driving north on I-35 to continue on I-135 but ended up on the Kansas Turnpike. Preparing for another trip north, where did we go wrong? Help, please.

Kansas Turnpike IS I-35 from the OK border to Emporia, then then it becomes I-335 to Topeka.

You must pay the part between the OK border to Wichita, and then get off to change to I-135 in Wichita. It should be very clear.

Well, I've been away from this board for awhile so I may be too late to answer this question. But, for what it's worth, driving north on I-35, you will want to exit at the South Wichita exit, where you will pay the toll. As the last poster stated, the turnpike starts at the Oklahoma border (but you get your turnpike ticket somewhere around Wellington), but when you exit at the South Wichita exit, it becomes I-135. Stay toward the right lane, because the left lane veers off to I-235 about a mile after the tollbooth. However, if you get stuck there, don't fear because 235 makes a loop around the west side of Wichita and eventually reconnects with 135.

As you got into Wichita, you should have followed the signs to Salina. That would have taken you through the tollbooth and onto the I35 route through the city. Move to the right as you leave the tollbooth.

You were "preparing for another trip north". How long did it take to figure out that its a toll road instead of troll road? Can you read road signs and maps? My ten year-old could figure this out.