In 1845 how did Portland, Oregon get its name?

It was a coin-toss!

William Overton and Asa Lovejoy (of Boston, MA), business partners in 1843, filed claim to the land (640 acres, 260 ha) on the Willamette River's west bank. At that stage, the area was a stopover for travelers between Oregon City and Fort Vancouver. The depth of the river was suitable for larger, ocean-going vessels.

Overton then sold his share of the claim to Francis W. Pettygrove of Portland, Maine.

When it came time to name their new town, Pettygrove and Lovejoy both had the same idea: to name it after his home town. They flipped a coin to decide, and Pettygrove won.

https://en.wikipedia.org/wiki/History_of_Portland,_Oregon