The Category Archive widget displays a monthly or yearly archive of posts for one specific category.
The WordPress Category Archive Widget Plugin displays a monthly or yearly archive of posts for one specific category. It is very similar to the WordPress Archive except that it just displays one specific category’s posts, not all categories. It can be configured to either show a listing or a dropdown by month or year with or without post counts.
1) Upload the plugin files to the /wp-content/plugins/category-archive-widget directory of your site or blog, or install the plugin through the WordPress plugins screen directly.
2) Activate the plugin through the ‘Plugins’ screen in WordPress
The Category Archive widget lets you show posts for one specific category. The built-in Archive widget shows posts for all categories.
If permalinks are on, the permalink structure must contain the category, year and month for the Category Archive widget to work properly (e.g. /%category%/%year%/%monthnum%/%post_id%/).