Susan,

Though the name is the same, the Lt. McGuire may or may not be your man. I did a quick search at Familysearch.org and found this listing from the 1880 Census for Roane County, TN.

Household:

Name Relation Marital Status Gender Race Age Birthplace Occupation Father's Birthplace Mother's Birthplace

Cornelius MC GUYRE Self M Male W 47 TN Wagoner TN TN
Polly MC GUYRE Wife M Female W 37 TN Keeping House VA VA
James MC GUYRE Son S Male W 18 TN Wagoner TN TN

Source Information:
Census Place District 13, Roane, Tennessee
Family History Library Film 1255275
NA Film Number T9-1275
Page Number 376D

Jim Martin