July-August for Ireland or?

We went for three weeks in July 2017 and had a lovely time. The weather was sunny most days and the crowds weren’t a problem.

We generally go either in April and May or in September/October......less crowds which are far more of a problem than weather. In our many trips there encompassing months we have only had 2-3 days where it was heavy rain all day making outdoor activity really hard. Most rainy days still have long stretches of no rain and Sun.....plus many times the rain is a light easy to cope with mist. Just be ready for it to change. Always remember my wife and I walking to McCarthys castle on the beach in Ballinskellig.....We got out of the car.....Not a cloud in the sky and it was so warm we left our hoodies in the car. Twenty minutes later we were being pelted by a cold fairly heavy rain....So we started back, by the time we reached the car it was absolutely gorgeous out again. That's Ireland......nothing really to worry about.

I was there in August, albeit 4-5 years ago. Crowds were not an issue.

Our experience mirrors that of ewewoolknit - several trips to Ireland during the shoulder seasons when we lived in the Pacific NW (so I feel your pain).
After a bit of trial and error we found that March was a bit too early for us weather wise, but that April and May were usually delightful. Suggest targeting April for your visit since it'll likely still be raining in Seattle and so you won't be missing anything at home. September/October are quite nice but as you know that's also prime time for outdoor activities in Washington state, so I'd probably stick to April. Will be a little cheaper and less crowded then too -the big rush doesn't really begin until the schools let out in June, when things can get very crowded indeed in popular places like Dublin and Kerry.

I’ve only gone in August, so I don’t know how to compare to “shoulder season”, but crowds were not an issue .

I was there in April and experienced weather that ran from almost cold enough to snow to warm enough to need a pair of shorts! But on average is was like most springs here in the northwest, wet and cool and Gortex recommended, but not really a problem.

Thank you, everyone!

We've made two trips in September (one stretched into early October) and found the weather to be quite nice. Septembers here in Portland are warmer than we experienced in Ireland but we didn't encounter anything much cooler than sweatshirt weather there. There were some cloudy or partly cloudy days, a couple of rainy days and a fair number of spectacular "blue sky-puffy white cloud" days. And, except for the weekend in Dublin, we didn't really run into tons of people. A lot depends on where you go--Galway, Dingle and Killarney aside, smaller towns and villages in the southwest and west tend not to be as crowded with tourists after the summer season ends.