Question
I live in Portland Oregon and want to replant my lawn. I plan on tilling and leveling it prior to planting. Is it to late to plant from seed?

Answer
First frost date in Multnomah County: October 30, according to data compiled by your Oregon Climate Service:

http://www.ocs.orst.edu/county_climate/Multnomah_files/Multnomah.html

Rule of Green Thumb:  If the ground is warm (i.e, no cooler than 60 degrees F), Cool Season Grass Seed will germinate.  Remember that Grass Seeds don't grow at the same rate.  Kentucky Bluegrass is the watched pot that never seems to boil in time; we sow Rye for its speedy Green.

BUT...!

that's merely the law of averages.  Your State Extension Service makes a clear point about that: Oregon is not your average state.  'Dates of last frost in Spring and first frost in Fall are not very useful because of the cool, rainy climate.'  Here's the URL:

http://extension.oregonstate.edu/coos/about/demographics.html

Your county is smack in the middle of their 'Willamette Valley Climate Division 2', says the National Climatic Data Center.  Their records say Portland hits 32 degrees for the first time by Oct. 31 only 20 percent of the time.  You stand a 50/50 chance of hitting 32 degrees by mid-November.  I can tell you, it's way too late here on Long Island (USDA Zone 7b) to plant a new Lawn, and my best guess says it is too late now to do anything much worth doing in Portland, too.

Lawn Seed sowed now may just not germinate until Spring.  Or you may get some freaky weather that grows Grass just long enough to kill most of it.  Given that you're not ready, I would postpone this work until Spring 2008.

Tilling and levelling should be done when the soil is as DRY as you can get it.  That may not happen where you are but if you can shoot for that you will minimize damage to the Soil.

That's my opinion.

Thanks for your question.