Google and other search engines offer an "Advanced Search" option that will limit results to a specific domain. Oftentimes, it is challenging to find a link to the Advanced Search on Google. If this is the case just search for "advanced search" in Google.
To limit to specific sites like .gov, type ".gov" into the "site or domain" field (screenshots below).
You can also limit in a regular google search by doing the following:
Put site:.gov after your search for government websites (see example below):
Put site:.edu after your search for higher education websites (see example below):
