FYI, GIS (Geographic Information System) data is a generic term that can include MANY types of data such as streets, property lines, corporate boundaries, digital terrain models, trails, hydrography, imagery, etc. You might get more helpful replies if you specify what types of data you are looking for.
It seems you are looking for property lines. I have yet to find property lines that are available for free download on a public data server. I won't say there are none out there, but likely you'll have to acquire the data from a local agency or consultant if any of have it in digital form. If none are available you may have to map the properties yourself from legal descriptions.
Neil Wilson (a.k.a. neilw) Infrastructure Suite/C3D 2013, LDT 2004, Power Civil v8i SS1 WIN 7 64 PRO HP Pavillion h8xt, i7 2600, 12 GB RADEON 6450, 1 GB http://www.sec-landmgt.com
For the last few years I have been working in two counties, each bordering the Ohio River on the south side. These two counties are one county apart, approx. 25 miles.
About 2 weeks ago I began playing with the National Map Viewer and was pleasantly surprised at the amount of data that I was getting on my home county. I moved to the other county to test it on an area and was just as surprised as before because there was practically nothing that was useful.
It appears that this is a work in progress. There are also maps available on this website showing what may be available and where.